vulkan: Possibly fix a compiler warning (-Wstrict-prototypes).
diff --git a/src/video/SDL_vulkan_internal.h b/src/video/SDL_vulkan_internal.h
index f38c5f8..cdf464e 100644
--- a/src/video/SDL_vulkan_internal.h
+++ b/src/video/SDL_vulkan_internal.h
@@ -81,8 +81,8 @@ extern SDL_bool SDL_Vulkan_GetInstanceExtensions_Helper(unsigned *userCount,
/* No SDL Vulkan support, just include the header for typedefs */
#include "SDL_vulkan.h"
-typedef void (*PFN_vkGetInstanceProcAddr) ();
-typedef int (*PFN_vkEnumerateInstanceExtensionProperties) ();
+typedef void (*PFN_vkGetInstanceProcAddr) (void);
+typedef int (*PFN_vkEnumerateInstanceExtensionProperties) (void);
#endif /* SDL_VIDEO_VULKAN */