ext4: avoid potential data overflow in next_linear_group

ext4: avoid potential data overflow in next_linear_group

ngroups is ext4_group_t (unsigned int) while next_linear_group treat it
in int. If ngroups is bigger than max number described by int, it will
be treat as a negative number. Then "return group + 1 >= ngroups ? 0 :
group + 1;" may keep returning 0.
Switch int to ext4_group_t in next_linear_group to fix the overflow.

Fixes: 196e402adf2e ("ext4: improve cr 0 / cr 1 group scanning")
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20230801143204.2284343-3-shikemeng@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>