phy: ti: dm816x: remove set but not used variable 'phy_data'

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

drivers/phy/ti/phy-dm816x-usb.c:192:29: warning:
 variable phy_data set but not used [-Wunused-but-set-variable]

It is never used, so can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>