fix another oob pointer arithmetic issue in printf floating point

this one could never cause any problems unless the compiler/machine
goes to extra trouble to break oob pointer arithmetic, but it's best
to fix it anyway.

src/stdio/vfprintf.c

@@ -319,7 +319,7 @@ static int fmt_fp(FILE *f, long double y, int w, int p, int fl, int t)
 	if (j < 9*(z-r-1)) {
 		uint32_t x;
 		/* We avoid C's broken division of negative numbers */
-		d = r + 1 + (j+9*LDBL_MAX_EXP)/9 - LDBL_MAX_EXP;
+		d = r + 1 + ((j+9*LDBL_MAX_EXP)/9 - LDBL_MAX_EXP);
 		j += 9*LDBL_MAX_EXP;
 		j %= 9;
 		for (i=10, j++; j<9; i*=10, j++);