ext4: use more strict checks for inodes_per_block on mount

[ Upstream commit cd6bb35bf7f6d7d922509bf50265383a0ceabe96 ]

Centralize the checks for inodes_per_block and be more strict to make
sure the inodes_per_block_group can't end up being zero.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>