test/buf-ring: skip test_full_page_reg() on HPPA

This test is doing a manual memory alignment to trigger an issue
in older kernels on getting -EFAULT when attempting to map them.
This doesn't really work on parisc, as we have strict alignment
concerns. So just skip this sub-test on hppa.

Signed-off-by: Jens Axboe <axboe@kernel.dk>