jfs: Fix sanity check in dbMount

[ Upstream commit 67373ca8404fe57eb1bb4b57f314cff77ce54932 ]

MAXAG is a legitimate value for bmp->db_numag

Fixes: e63866a47556 ("jfs: fix out-of-bounds in dbNextAG() and diAlloc()")

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit ea462ee11dbc4eb779146313d3abf5e5187775e1)
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>