usb: musb: register nop transceiver driver for jz4740

Following the name change of the NOP transceiver driver in commit
4525beeb (usb: phy: rename usb_nop_xceiv to usb_phy_generic), the
transceiver driver was no longer operable under its old name.

Register the transceiver driver before calling usb_get_phy() to make
sure we are noticed by an error message if it is not available.

Signed-off-by: Apelete Seketeli <apelete@seketeli.net>
Signed-off-by: Felipe Balbi <balbi@ti.com>