usb: musb: avoid FADDR read access

This is part of the workaround for AM35x advisory Advisory 1.1.20.
The advisory says that the IPSS bridge can't handle 8 & 16 bit read
access. An 8bit read access to FADDR results in an 32bit read
access which also reads INTRTX and therefore may lose interrupts.
This patch removes any reads to FADDR as they are not really required.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>