fs: Drop unlikely before IS_ERR(_OR_NULL)

IS_ERR(_OR_NULL) already contain an 'unlikely' compiler flag and there
is no need to do that again from its callers. Drop it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Jeff Layton <jlayton@poochiereds.net>
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steve French <smfrench@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>