drm/tests/buddy: fix build with unused prng

drm/tests/buddy: fix build with unused prng

We no longer use the prng, which leads to the following warning:

drivers/gpu/drm/tests/drm_buddy_test.c: In function
‘drm_test_buddy_alloc_clear’:
drivers/gpu/drm/tests/drm_buddy_test.c:264:23: error: unused variable
‘prng’ [-Werror=unused-variable]
  264 |         DRM_RND_STATE(prng, random_seed);

v2 (Thomas)
 - Add Closes links

Reported-by: Jani Nikula <jani.nikula@intel.com>
Closes: https://lore.kernel.org/dri-devel/875xmggvcs.fsf@intel.com/
Reported-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Closes: https://lore.kernel.org/dri-devel/3f816555e6913fdbcb254523f65c98088d70581b.camel@intel.com/
Fixes: 8cb3a1e2b350 ("drm/buddy: Add a testcase to verify the multiroot fini")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250115124941.155990-2-matthew.auld@intel.com