btrfs/290: Make the test compatible with all supported block sizes

btrfs/290: Make the test compatible with all supported block sizes

This test fails with 64k block size with the following error:

     punch
     pread: Input/output error
     pread: Input/output error
    +ERROR: couldn't find extent 4096 for inode 261
     plug
    -pread: Input/output error
    -pread: Input/output error
    ...

The reason is that, some of the subtests are written with 4k blocksize
in mind. Fix the test by making the offsets and sizes to multiples of
64k so that it becomes compatible/aligned with all supported block sizes.

Reported-by: Disha Goel <disgoel@linux.ibm.com>
Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>