ext4: improve error msg for ext4_mb_seq_groups_show

While cat mb_groups for a mounted ext4 image which has some corrupted
group, the string return to userspace was just "I/O error" which confuse
me a lot. Improve it with ext4_decode_error.

Signed-off-by: yangerkun <yangerkun@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240118042557.380058-2-yangerkun@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>