usb: Use get_unaligned() in usb_endpoint_maxp() for wMaxPacketSize

usb: Use get_unaligned() in usb_endpoint_maxp() for wMaxPacketSize

Use unaligned access to fetch wMaxPacketSize in usb_endpoint_maxp()
api.
In its absence we see following data abort message:
==============================================================
data abort

    MAYBE you should read doc/README.arm-unaligned-accesses

pc : [<bf794e24>]          lr : [<bf794e1c>]
sp : bf37c7b0  ip : 0000002f     fp : 00000000
r10: 00000000  r9 : 00000002     r8 : bf37fecc
r7 : 00000001  r6 : bf7d8931     r5 : bf7d891c  r4 : bf7d8800
r3 : bf7d65b0  r2 : 00000002     r1 : bf7d65b4  r0 : 00000027
Flags: nZCv  IRQs off  FIQs off  Mode SVC_32
Resetting CPU ...

resetting ...
==============================================================

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Cc: Ilya Yanok <ilya.yanok@cogentembedded.com>
Cc: Marek Vasut <marex@denx.de>