usb: phy: mv-usb: Remove set but not used variable 'phy'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/usb/phy/phy-mv-usb.c: In function mv_otg_work:
drivers/usb/phy/phy-mv-usb.c:404:18: warning: variable phy set but not used [-Wunused-but-set-variable]

It's no used since commit e47d9254 ("usb: move
the OTG state from the USB PHY to the OTG structure")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>