broadcom/vc4: Fix aliasing issue

This was causing Android clang version 3.8.256229 to miscompile,
presumably due to strict aliasing.

Fixes: 14dc281c13 ("vc4: Enforce one-uniform-per-instruction after optimization.")

src/gallium/drivers/vc4/vc4_qir_lower_uniforms.c

@@ -66,7 +66,7 @@ remove_uniform(struct hash_table *ht, struct qreg reg)
 
         entry = _mesa_hash_table_search(ht, key);
         assert(entry);
-        entry->data--;
+        entry->data = (void *)(((uintptr_t) entry->data) - 1);
         if (entry->data == NULL)
                 _mesa_hash_table_remove(ht, entry);
 }