Fix GPU build error after recent commit.

source/blender/gpu/GPU_extensions.h

@@ -42,6 +42,7 @@ bool GPU_full_non_power_of_two_support(void);
 bool GPU_bicubic_bump_support(void);
 
 int GPU_max_texture_size(void);
+int GPU_max_texture_layers(void);
 int GPU_max_textures(void);
 float GPU_max_texture_anisotropy(void);
 int GPU_max_color_texture_samples(void);

source/blender/gpu/intern/gpu_texture.c

@@ -160,6 +160,8 @@ static int gpu_get_component_count(GPUTextureFormat format)
 /* Definitely not complete, edit according to the gl specification. */
 static void gpu_validate_data_format(GPUTextureFormat tex_format, GPUDataFormat data_format)
 {
+	(void)data_format;
+
 	if (ELEM(tex_format,
 	         GPU_DEPTH_COMPONENT24,
 	         GPU_DEPTH_COMPONENT16,