tty: Avoid the use of one-element arrays

One-element arrays are being deprecated[1]. Replace the one-element arrays
with simple value types 'char reserved_char' and 'compat_int_t reserved'[2],
once it seems these are just placeholders for alignment.

Also, while there, use the preferred form for passing a size of a struct.
The alternative form where struct name is spelled out hurts readability
and introduces an opportunity for a bug when the variable type is changed
but the corresponding sizeof that is passed as argument is not.

Lastly, fix the checkpatch.pl warnings below:

ERROR: code indent should use tabs where possible
+        char    reserved_char;$

WARNING: please, no spaces at the start of a line
+        char    reserved_char;$

ERROR: code indent should use tabs where possible
+        compat_int_t    reserved;$

WARNING: please, no spaces at the start of a line
+        compat_int_t    reserved;$

[1] KSPP#79
[2] KSPP#86

Tested-by: kernel test robot <lkp@intel.com>
Link: https://github.com/GustavoARSilva/linux-hardening/blob/master/cii/0-day/tty-20200716.md
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/tty/tty_io.c

@@ -2683,15 +2683,15 @@ struct serial_struct32 {
         compat_int_t    baud_base;
         unsigned short  close_delay;
         char    io_type;
-        char    reserved_char[1];
+	char    reserved_char;
         compat_int_t    hub6;
         unsigned short  closing_wait; /* time to wait before closing */
         unsigned short  closing_wait2; /* no longer used... */
         compat_uint_t   iomem_base;
         unsigned short  iomem_reg_shift;
         unsigned int    port_high;
      /* compat_ulong_t  iomap_base FIXME */
-        compat_int_t    reserved[1];
+	compat_int_t    reserved;
 };
 
 static int compat_tty_tiocsserial(struct tty_struct *tty,
@@ -2705,7 +2705,7 @@ static int compat_tty_tiocsserial(struct tty_struct *tty,
 	struct serial_struct v;
 	int flags;
 
-	if (copy_from_user(&v32, ss, sizeof(struct serial_struct32)))
+	if (copy_from_user(&v32, ss, sizeof(*ss)))
 		return -EFAULT;
 
 	memcpy(&v, &v32, offsetof(struct serial_struct32, iomem_base));
@@ -2743,7 +2743,7 @@ static int compat_tty_tiocgserial(struct tty_struct *tty,
 			0xfffffff : ptr_to_compat(v.iomem_base);
 		v32.iomem_reg_shift = v.iomem_reg_shift;
 		v32.port_high = v.port_high;
-		if (copy_to_user(ss, &v32, sizeof(struct serial_struct32)))
+		if (copy_to_user(ss, &v32, sizeof(v32)))
 			err = -EFAULT;
 	}
 	return err;