gl_common: demote uniform location get failure log

If the user is using custom shaders, picom will naturally fail to get
some uniform locations if the given uniform is not used in the shader.
So we really shouldn't report error for it.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/gl/gl_common.c

@@ -50,8 +50,8 @@ struct gl_blur_context {
 static GLint glGetUniformLocationChecked(GLuint p, const char *name) {
 	auto ret = glGetUniformLocation(p, name);
 	if (ret < 0) {
-		log_error("Failed to get location of uniform '%s'. the compositor might "
-		          "not work correctly.",
+		log_info("Failed to get location of uniform '%s'. This is normal when "
+		         "using custom shaders.",
 		         name);
 	}
 	return ret;