radv: fix detecting FMASK_DECOMPRESS/DCC_DECOMPRESS meta pipelines

radv: fix detecting FMASK_DECOMPRESS/DCC_DECOMPRESS meta pipelines

With the on_demand shaders feature, meta pipelines are only created
when they are used, otherwise they are NULL. Though, inside secondary
cmdbuffers, the graphics pipeline might be also NULL. In this specific
case, radv_is_{dcc,fmask}_decompress_pipeline() would return
TRUE because these pipelines are NULL too...

This fixes flakes with tests that use secondary cmdbuffers with
TC-compat images.

Cc: mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22440>