mvtwsi: Fix breakage introduced by "Fix mvtwsi not working on sun6i and newer sunxi SoCs"

"Fix mvtwsi not working on sun6i and newer sunxi SoCs" includes the following:

@@ -189,7 +200,8 @@ static int twsi_start(struct i2c_adapter *adap, int expected_status)
 	/* globally set TWSIEN in case it was not */
 	twsi_control_flags |= MVTWSI_CONTROL_TWSIEN;
 	/* assert START */
-	writel(twsi_control_flags | MVTWSI_CONTROL_START, &twsi->control);
+	twsi_control_flags |= MVTWSI_CONTROL_START | MVTWSI_CONTROL_CLEAR_IFLG;
+	writel(twsi_control_flags, &twsi->control);
 	/* wait for controller to process START */
 	return twsi_wait(adap, expected_status);
 }

The modification of twsi_control_flags done here was introduced while
merging to fix a line > 80 chars, but twsi_control_flags is a global variable
and should not be modified like this here, this commit fixes this, restoring
mvtwsi functionality.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>