Fix off-by-one error in processing of #ifdef lines

The convention in this program is to parse the line immediately starting
after the token (e.g. #defineA and #ifdefA define respectively look-up "A"),
and this commit restores this behavior instead of skipping an assumed
white-space character following #ifdef.

Reported by:	kevans
MFC after:	3 days

usr.bin/calendar/io.c

@@ -213,7 +213,7 @@ token(char *line, FILE *out, bool *skip)
 	}
 
 	if (strncmp(line, "ifdef", 5) == 0) {
-		walk = line + 6;
+		walk = line + 5;
 		trimlr(&walk);
 
 		if (*walk == '\0') {