gfs2: Use uid_eq and gid_eq where appropriate

Where kuid_t values are compared use uid_eq and where kgid_t values
are compared use gid_eq.  This is unfortunately necessary because
of the type safety that keeps someone from accidentally mixing
kuids and kgids with other types.

Cc: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>