radv/extensions: fix c_vk_version for patch == None

radv/extensions: fix c_vk_version for patch == None

Similar to cb0d1ba156 ("anv/extensions: Fix VkVersion::c_vk_version for patch == None")
fixes the following building errors:

out/target/product/x86_64/obj_x86/STATIC_LIBRARIES/libmesa_radv_common_intermediates/radv_entrypoints.c:1161:48:
error: use of undeclared identifier 'None'; did you mean 'long'?
      return instance && VK_MAKE_VERSION(1, 0, None) <= core_version;
                                               ^~~~
                                               long
external/mesa/include/vulkan/vulkan.h:34:43: note: expanded from macro 'VK_MAKE_VERSION'
    (((major) << 22) | ((minor) << 12) | (patch))
                                          ^
...
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.

Fixes: e72ad05c1d ("radv: Return NULL for entrypoints when not supported.")
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>