SELinux: standardize return code handling in selinuxfs.c

selinuxfs.c has lots of different standards on how to handle return paths on
error.  For the most part transition to

	rc=errno
	if (failure)
		goto out;
[...]
out:
	cleanup()
	return rc;

Instead of doing cleanup mid function, or having multiple returns or other
options.  This doesn't do that for every function, but most of the complex
functions which have cleanup routines on error.
Signed-off-by: NEric Paris <eparis@redhat.com>