pan/decode: Remove SHORT_SLIDE indirection

pan/decode: Remove SHORT_SLIDE indirection

../src/panfrost/pandecode/decode.c: In function ‘pandecode_compute_fbd’:
../src/panfrost/pandecode/decode.c:789:35: warning: taking address of packed member of ‘struct mali_compute_fbd’ may result in an unaligned pointer value [-Waddress-of-packed-member]
  789 |         pandecode_u32_slide(num, s->unknown ## num, ARRAY_SIZE(s->unknown ## num))
      |                                  ~^~~~~~~~~
../src/panfrost/pandecode/decode.c:800:9: note: in expansion of macro ‘SHORT_SLIDE’
  800 |         SHORT_SLIDE(1);
      |         ^~~~~~~~~~~

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3543>