phy: phy-imx8mq-usb: Remove .exit operation

Currently, when running "ums 0 mmc 2" and breaking it via
CTRL + C, the following message is seen:

u-boot=> ums 0 mmc 1
UMS: LUN 0, dev mmc 1, hwpart 0, sector 0x0, count 0x1dacc00
CTRL+C - Operation aborted
clk usb_phy_root_clk already disabled

The USB PHY clock is disabled twice: first it gets disabled
inside imx8mq_usb_phy_power_off(), then it is disabled again
inside imx8mq_usb_phy_exit().

Let the USB PHY clock be disabled only once inside
imx8mq_usb_phy_power_off() by removing the .exit operation.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/phy/phy-imx8mq-usb.c b/drivers/phy/phy-imx8mq-usb.c
index b660ead..e5e96e7 100644
--- a/drivers/phy/phy-imx8mq-usb.c
+++ b/drivers/phy/phy-imx8mq-usb.c
@@ -231,16 +231,10 @@
 	return 0;
 }
 
-static int imx8mq_usb_phy_exit(struct phy *usb_phy)
-{
-	return imx8mq_usb_phy_power_off(usb_phy);
-}
-
 struct phy_ops imx8mq_usb_phy_ops = {
 	.init = imx8mpq_usb_phy_init,
 	.power_on = imx8mq_usb_phy_power_on,
 	.power_off = imx8mq_usb_phy_power_off,
-	.exit = imx8mq_usb_phy_exit,
 };
 
 int imx8mq_usb_phy_probe(struct udevice *dev)