quota: Silence warning about PRJQUOTA not being handled in need_print_warning()

PRJQUOTA value of quota type should never reach need_print_warning() since XFS
(which is the only fs which uses that type) doesn't use generic functions
calling this function. Anyway, add PRJQUOTA case to the switch to make gcc
happy.

Signed-off-by: Jan Kara <jack@suse.cz>