minikconf: fix parser typo

The result of this typo would be that "select_foo" would be treated as a "select"
keyword followed by "_foo".  Nothing too bad, but easy to fix so let's be clean.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

scripts/minikconf.py

@@ -592,7 +592,7 @@ class KconfigParser:
         if not self.src.startswith(rest, self.cursor):
             return False
         length = len(rest)
-        if self.src[self.cursor + length].isalnum() or self.src[self.cursor + length] == '|':
+        if self.src[self.cursor + length].isalnum() or self.src[self.cursor + length] == '_':
             return False
         self.cursor += length
         return True