generic/285: fix test for generic SEEK_HOLE/DATA implementations

generic/285: fix test for generic SEEK_HOLE/DATA implementations

Generic implementation of SEEK_HOLE/DATA reports whole file as data chunk with
virtual hole at the end (generic_file_llseek, used by ext2/ext3/reiserfs/nfs).

Currently test prepares file smaller than expected for "huge file" testcases
(testcases 10-12). This patch fixes test file layout, now second data chunk
ends right at the expected end of file.

Plus it fixes type of 'filesz' argument, it should be off_t.

Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@samsung.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>