Revert "ext4: remove unnecessary check in ext4_bg_num_gdb_nometa"

Revert "ext4: remove unnecessary check in ext4_bg_num_gdb_nometa"

This reverts commit ad3f09be6cfe332be8ff46c78e6ec0f8839107aa.

The reverted commit was intended to simpfy the code to get group
descriptor block number in non-meta block group by assuming
s_gdb_count is block number used for all non-meta block group descriptors.
However s_gdb_count is block number used for all meta *and* non-meta
group descriptors. So s_gdb_group will be > actual group descriptor block
number used for all non-meta block group which should be "total non-meta
block group" / "group descriptors per block", e.g. s_first_meta_bg.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Link: https://lore.kernel.org/r/20230613225025.3859522-1-shikemeng@huaweicloud.com
Fixes: ad3f09be6cfe ("ext4: remove unnecessary check in ext4_bg_num_gdb_nometa")
Cc: stable@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>