emulators/snes9x-gtk: fix build on 32-bits

/wrkdirs/usr/ports/emulators/snes9x-gtk/work/snes9x-1.63/gtk/src/gtk_display_driver_vulkan.cpp:69:54: error: assigning to 'VkDescriptorPool' (aka 'unsigned long long') from incompatible type 'vk::DescriptorPool'

69 |     init_info.DescriptorPool = imgui_descriptor_pool.get();
   |                                ~~~~~~~~~~~~~~~~~~~~~~^~~~~

/wrkdirs/usr/ports/emulators/snes9x-gtk/work/snes9x-1.63/gtk/src/gtk_display_driver_vulkan.cpp:74:5: error: no matching function for call to 'ImGui_ImplVulkan_Init'

74 |     ImGui_ImplVulkan_Init(&init_info, context->swapchain->get_render_pass());
   |     ^~~~~~~~~~~~~~~~~~~~~

/wrkdirs/usr/ports/emulators/snes9x-gtk/work/snes9x-1.63/gtk/../external/imgui/imgui_impl_vulkan.h:67:29: note: candidate function not viable: no known conversion from 'vk::RenderPass' to 'VkRenderPass' (aka 'unsigned long long') for 2nd argument

67 | IMGUI_IMPL_API bool         ImGui_ImplVulkan_Init(ImGui_ImplVulkan_InitInfo* info, VkRenderPass render_pass);
   |                             ^                                                      ~~~~~~~~~~~~~~~~~~~~~~~~

1 warning and 2 errors generated.