anv: Silence a couple compiler warnings

anv: Silence a couple compiler warnings

[63/93] Compiling C object 'src/intel/vulkan/...intel@vulkan@@anv_common@sta/anv_device.c.o'.
../src/intel/vulkan/anv_device.c:685:30: warning: passing 'const char *' to parameter of type 'void *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
   vk_free(&instance->alloc, instance->app_info.app_name);
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~
../src/vulkan/util/vk_alloc.h:62:51: note: passing argument to parameter 'data' here
vk_free(const VkAllocationCallbacks *alloc, void *data)
                                                  ^
../src/intel/vulkan/anv_device.c:686:30: warning: passing 'const char *' to parameter of type 'void *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
   vk_free(&instance->alloc, instance->app_info.engine_name);
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../src/vulkan/util/vk_alloc.h:62:51: note: passing argument to parameter 'data' here
vk_free(const VkAllocationCallbacks *alloc, void *data)
                                                  ^
[65/93] Compiling C object 'src/intel/vulkan/...ommon@sta/anv_nir_apply_pipeline_layout.c.o'.
../src/intel/vulkan/anv_nir_apply_pipeline_layout.c:519:13: warning: unused variable 'image_uniform' [-Wunused-variable]
   unsigned image_uniform;

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>