Fix __attribute__ usage

Requires two sets of parentheses, not one.  ...I think

libobs/util/c99defs.h

@@ -24,7 +24,7 @@
 #ifdef _MSC_VER
 #define FORCE_INLINE __forceinline
 #else
-#define FORCE_INLINE __attribute__(always_inline)
+#define FORCE_INLINE __attribute__((always_inline))
 #endif
 
 #ifdef _MSC_VER