HPFS: Restrict uid and gid to 16-bit values

Restrict uid and gid to 16-bit values.

HPFS stores only 2 bytes in the EAs.

Signed-off-by: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>