abs() is abs and should work as abs when you want abs

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@1056 a1c6a512-1295-4272-9138-f99709370657

firmware/include/stdlib.h

@@ -30,7 +30,7 @@ void *calloc (size_t nmemb, size_t size);
 void free(void *);
 void *realloc(void *, size_t);
 
-#define abs(x) ((x)>0?x:-x)
+#define abs(x) ((x)>0?(x):-(x))
 
 #ifdef __cplusplus
 }