uio-howto: example bug

Bug in demo program, checking wrong return value
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Cc: "Hans J. Koch" <hjk@hansjkoch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/DocBook/uio-howto.tmpl

@@ -984,7 +984,7 @@ int main()
 		return errno;
 	}
 	configfd = open("/sys/class/uio/uio0/device/config", O_RDWR);
-	if (uiofd < 0) {
+	if (configfd < 0) {
 		perror("config open:");
 		return errno;
 	}