ext4/021: check _scratch_mkfs_sized return code

ext4/021: check _scratch_mkfs_sized return code

The test cases ext4/021 calls _scratch_mkfs before _scratch_mkfs_sized,
and does not check return code of _scratch_mkfs_sized. Even if
_scratch_mkfs_sized failed, _scratch_mount after it cannot detect the
sized mkfs failure because _scratch_mkfs already created a file system
on the device. This results in unexpected test condition.

To avoid the unexpected test condition, check return code of
_scratch_mkfs_sized.

Suggested-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>