fastboot: OUT transaction length must be aligned to wMaxPacketSize

fastboot: OUT transaction length must be aligned to wMaxPacketSize

OUT transactions must be aligned to wMaxPacketSize for each transfer,
or else transfer will not complete successfully. This patch modifies
rx_bytes_expected to return a transfer length that is aligned to
wMaxPacketSize.

Note that the value of wMaxPacketSize and ep->maxpacket may not be
the same value, and it is the value of wMaxPacketSize that should be
used for alignment. wMaxPacketSize is passed depending on the speed of
connection.

Signed-off-by: Dileep Katta <dileep.katta@linaro.org>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>