usb: phy: protect against NULL phy pointers
usb: phy: protect against NULL phy pointers

In order to decrease the amount of work done
by PHY users, allow NULL phy pointers to be
passed.

Signed-off-by: Felipe Balbi <94dddeeef08b001e003cce128ddc162a4e2c6cd2@ti.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs