staging: mt7621-pci-phy: remove disable clock from the phy exit function

The clock which has been used here is not about the phy but the pcie port.
It has been properly handled into host pcie driver code. Hence, remove it
from here which is the correct thing to do.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>