radv/meta_decompress: fix pointer to integer conversion

radv/meta_decompress: fix pointer to integer conversion

VK_NULL_HANDLE replaces NULL to avoid following building error:

external/mesa/src/amd/vulkan/radv_meta_decompress.c:365:54: error:
incompatible pointer to integer conversion passing 'void *' to parameter
of type 'VkShaderModule' (aka 'unsigned long long') [-Werror,-Wint-conversion]
                VkResult ret = create_pipeline(cmd_buffer->device, NULL, samples,
                                                                   ^~~~
prebuilts/clang/host/linux-x86/clang-4053586/lib64/clang/5.0.300080/include/stddef.h:105:16:
note: expanded from macro 'NULL'
#  define NULL ((void*)0)
               ^~~~~~~~~~
external/mesa/src/amd/vulkan/radv_meta_decompress.c:97:32:
note: passing argument to parameter 'vs_module_h' here
                VkShaderModule vs_module_h,
                               ^
1 error generated.

Fixes: fbcd167314 ("radv: Add on-demand compilation of built-in shaders.")
Signed-off-by: Mauro Rossi <issor.oruam@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>