TT#111150 Remove range check that is always true in phone_digit_hex()

We have already compared for d being less or equal than 9.

Change-Id: I26a9e95b786efa17537d8a5484688c1322ba2f42
Warned-by: lgtm

src/tcap.c

@@ -397,7 +397,7 @@ static inline char phone_digit(unsigned char d) {
 static inline char phone_digit_hex(unsigned char d) {
 	if (d <= 9)
 		return '0' + d;
-	else if (d >= 10 && d <= 15)
+	else if (d <= 15)
 		return 'A' + d - 10;
 	return '?';
 }