generic/275: fix on 32k fsblock filesystems

generic/275: fix on 32k fsblock filesystems

This test fails on 32k-fsblock filesystems:

dd: failed to open '/opt/tmp3': No space left on device
dd: failed to open '/opt/tmp4': No space left on device
Pre rm space:
Filesystem     Type 1024-blocks    Used Available Capacity Mounted on
/dev/sda4      xfs      2031616 2030624       992     100% /opt
Post rm space:
Filesystem     Type 1024-blocks    Used Available Capacity Mounted on
/dev/sda4      xfs      2031616 2030368      1248     100% /opt
could not sufficiently fill filesystem

On a 32k-fsblock filesystem, creating tmp3 and tmp4 requires more than
1MB for the transaction allocation, which is why this test fails to fill
the filesystem.  To fix this, touch the four tmp files before trying to
use up all the free space.  The fix in ef25a29fa49a50 was incomplete.

Cc: fstests@vger.kernel.org # v2022.07.24
Fixes: ef25a29fa49a50 ("generic/275: fix premature enospc errors when fs block size is large")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Zorro Lang <zlang@kernel.org>