usb: ulpi: Fix compile warning in read/write on 64-bit machines.

usb: ulpi: Fix compile warning in read/write on 64-bit machines.

ulpi_read and ulpi_write are used to read/write registers via ULPI bus.
Code generates compilation warnings on 64-bit machines where pointer
is cast to u32.

This patch drops all but last 8 bits of register address.
It is possible, because addresses on ULPI bus are 6- or 8-bit.

It is not possible (according to ULPI 1.1 spec) to have more
than 8-bit addressing.

This patch should not cause regressions as all calls to
ulpi_read/write use either structure pointer (@ address 0) or integer
offsets cast to pointer - addresses requested are way below 8-bit range.

Signed-off-by: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
Acked-by: Marek Vasut <marex@denx.de>