radv: Use a fallback for marketing name when libdrm doesn't know it.

Currently for GPUs which don't have a marketing name in libdrm,
RADV just prints "(null) (RADV ...)", which looks bad.

This commit replaces the "(null)" with "AMD Unknown".

Cc: mesa-stable
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18775>

src/amd/vulkan/radv_device.c

@@ -815,7 +815,8 @@ radv_physical_device_try_create(struct radv_instance *instance, drmDevicePtr drm
 
    const char *marketing_name = device->ws->get_chip_name(device->ws);
    snprintf(device->marketing_name, sizeof(device->name), "%s (RADV %s%s)",
-            marketing_name, device->rad_info.name, radv_get_compiler_string(device));
+            marketing_name ? marketing_name : "AMD Unknown", device->rad_info.name,
+            radv_get_compiler_string(device));
 
 #ifdef ENABLE_SHADER_CACHE
    if (radv_device_get_cache_uuid(device, device->cache_uuid)) {