Fix the invalid variable issue when set-fips in uboot (#2834)

What I did
Reproduce the issue:

/home/admin# sonic-installer set-fips
Command: /usr/bin/fw_setenv linuxargs net.ifnames=0 loopfstype=squashfs loop=image-20220531.27/fs.squashfs systemd.unified_cgroup_hierarchy=0 varlog_size=4096 loglevel=4 sonic_fips=1
Error: illegal character '=' in variable name "loopfstype=squashfs"

Work item tracking
Microsoft ADO (number only): 22333116
How I did it
Add the double quotation marks when calling the command.

How to verify it
It works fine when calling the following command:
/usr/bin/fw_setenv linuxargs "net.ifnames=0 loopfstype=squashfs loop=image-20220531.27/fs.squashfs systemd.unified_cgroup_hierarchy=0 varlog_size=4096 loglevel=4 sonic_fips=1"

sonic_installer/bootloader/uboot.py

@@ -89,7 +89,8 @@ def set_fips(self, image, enable):
         cmdline = out.strip()
         cmdline = re.sub('^linuxargs=', '', cmdline)
         cmdline = re.sub(r' sonic_fips=[^\s]', '', cmdline) + " sonic_fips=" + fips
-        run_command('/usr/bin/fw_setenv linuxargs ' +  cmdline)
+        cmdline = '"' + cmdline + '"'
+        run_command('/usr/bin/fw_setenv linuxargs ' +  cmdline )
         click.echo('Done')
 
     def get_fips(self, image):