intel/blorp: Fix usage of uninitialized memory in key hashing

intel/blorp: Fix usage of uninitialized memory in key hashing

The automatically generated padding in structs contains
undefined values, force pack the structs to eliminate the
padding. Otherwise structs with the same values may generate
different hashes.

Valgrind output:

Conditional jump or move depends on uninitialised value(s)
 util_fast_urem32 (fast_urem_by_const.h:71)
 hash_table_search (hash_table.c:262)
 _mesa_hash_table_search (hash_table.c:296)
 anv_pipeline_cache_search_locked (anv_pipeline_cache.c:318)
 anv_pipeline_cache_search (anv_pipeline_cache.c:335)
 lookup_blorp_shader (anv_blorp.c:38)
 blorp_params_get_mcs_partial_resolve_kernel (blorp_clear.c:1112)
 blorp_mcs_partial_resolve (blorp_clear.c:1205)
 anv_image_mcs_op (anv_blorp.c:1742)
 anv_cmd_predicated_mcs_resolve (genX_cmd_buffer.c:774)
 transition_color_buffer (genX_cmd_buffer.c:1159)
 cmd_buffer_end_subpass (genX_cmd_buffer.c:4840)

Uninitialised value was created by a stack allocation
 blorp_params_get_mcs_partial_resolve_kernel (blorp_clear.c:1103)

Cc: <mesa-stable@lists.freedesktop.org>
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>