avutil/hwcontext_vulkan: Query the correct format

In the call to vkGetPhysicalDeviceImageFormatProperties2(), we were
previously requesting the properties of the first fallback format (e.g.
VK_FORMAT_R8_UNORM for VK_FORMAT_G8_B8R8_2PLANE_420_UNORM) instead of
the actual format in use.

We don’t do anything with it afterwards, but there is no reason to keep
querying the wrong format.

libavutil/hwcontext_vulkan.c

@@ -2590,7 +2590,7 @@ static void try_export_flags(AVHWFramesContext *hwfc,
     VkPhysicalDeviceImageFormatInfo2 pinfo = {
         .sType  = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_IMAGE_FORMAT_INFO_2,
         .pNext  = !exp ? NULL : &enext,
-        .format = av_vkfmt_from_pixfmt(hwfc->sw_format)[0],
+        .format = vk_find_format_entry(hwfc->sw_format)->vkf,
         .type   = VK_IMAGE_TYPE_2D,
         .tiling = hwctx->tiling,
         .usage  = hwctx->usage,