lib/vsprintf.c: replace while with do-while in skip_atoi

All callers of skip_atoi have already checked for the first character
being a digit.  In this case, gcc generates simpler code for a do
while-loop.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/vsprintf.c

@@ -114,8 +114,9 @@ int skip_atoi(const char **s)
 {
 	int i = 0;
 
-	while (isdigit(**s))
+	do {
 		i = i*10 + *((*s)++) - '0';
+	} while (isdigit(**s));
 
 	return i;
 }