math: fix nextafter definition in tgmath.h

include/tgmath.h

@@ -230,7 +230,7 @@ sizeof(double) == sizeof(long double)
 #define lrint(x)        __tg_real(lrint, (x))
 #define lround(x)       __tg_real(lround, (x))
 #define nearbyint(x)    __tg_real(nearbyint, (x))
-#define nextafter(x,y)  __tg_real_2(nextafter, (x), (y)
+#define nextafter(x,y)  __tg_real_2(nextafter, (x), (y))
 #define nexttoward(x,y) __tg_real_2(nexttoward, (x), (y))
 #define pow(x,y)        __tg_real_complex_pow((x), (y))
 #define remainder(x,y)  __tg_real_2(remainder, (x), (y))