vulkan/util: Fix implicit declaration of ffs for Android build

Similar to 641320ce02 and 68bb26af63 to avoid Android build errors

Fixes the following building error:

In file included from external/mesa/src/vulkan/util/vk_util.c:28:
external/mesa/src/vulkan/util/vk_util.h:248:30: error: implicit declaration of function 'ffs' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
   return (gl_shader_stage) (ffs((uint32_t) vk_stage) - 1);
                             ^
1 error generated.

Fixes: 06ebbde630 ("vulkan: Deduplicate mesa stage conversion")
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10023>

src/vulkan/util/vk_util.h

@@ -23,6 +23,7 @@
 #ifndef VK_UTIL_H
 #define VK_UTIL_H
 
+#include "util/bitscan.h"
 #include "util/macros.h"
 #include "compiler/shader_enums.h"
 #include <string.h>