MINOR: tools: don't use unlikely() in hex2i()

This small inline function causes some pain to the compiler when used
inside other functions due to its use of the unlikely() hint for non-digits.
It causes the letters to be processed far away in the calling function and
makes the code less efficient. Removing these unlikely() hints has increased
the chunk size parsing by around 5%.
diff --git a/include/common/standard.h b/include/common/standard.h
index a06fb84..d88599d 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -317,9 +317,9 @@
  */
 static inline int hex2i(int c)
 {
-	if (unlikely((unsigned char)(c -= '0') > 9)) {
-		if (likely((unsigned char)(c -= 'A' - '0') > 5 &&
-			      (unsigned char)(c -= 'a' - 'A') > 5))
+	if ((unsigned char)(c -= '0') > 9) {
+		if ((unsigned char)(c -= 'A' - '0') > 5 &&
+			      (unsigned char)(c -= 'a' - 'A') > 5)
 			c = -11;
 		c += 10;
 	}