sx.c: fix missed unlock_kernel() on error path in sx_fw_ioctl()

If we return directly with -EPERM then lock_kernel() is still held.

This was found with a code checker (http://repo.or.cz/w/smatch.git/).

[akpm@linux-foundation.org: fix another such path - missed func_exit()]
Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: <R.E.Wolff@BitWizard.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>