usb/config: use proper endian access for wMaxPacketSize

wMaxPacketSize is __le16 and should be accessed as such. Also fix the
wBytesPerInterval assignment while here.

v2: also fix the wBytesPerInterval assigment, noticed by Matt Evans

This patch should be backported to the 3.0 kernel.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Acked-by: Matt Evans <matt@ozlabs.org>
Cc: stable@kernel.org