src/: Simplify, using strpbrk(3)

Comparing against NULL is more readable than comparing against a length.

This removes the only uses of strcspn(3) in this project.  strpbrk(3) is
a simpler call, even though it has a weird name.  It's just like
strchr(3) but searches for several characters.  I'd have named it
strchrs().

Signed-off-by: Alejandro Colomar <alx@kernel.org>

src/useradd.c

@@ -109,7 +109,7 @@ static const char *def_log_init = "yes";
 static long def_inactive = -1;
 static const char *def_expire = "";
 
-#define	VALID(s)	(strcspn (s, ":\n") == strlen (s))
+#define	VALID(s)	(strpbrk(s, ":\n") == NULL)
 
 static const char *user_name = "";
 static const char *user_pass = "!";

src/usermod.c

@@ -93,7 +93,7 @@
 #define E_SUB_GID_UPDATE 18	/* can't update the subordinate gid file */
 #endif				/* ENABLE_SUBIDS */
 
-#define	VALID(s)	(strcspn (s, ":\n") == strlen (s))
+#define	VALID(s)	(strpbrk(s, ":\n") == NULL)
 
 /*
  * Global variables