usb: fix unaligned access in device_qual()

usb: fix unaligned access in device_qual()

while playing with dfu, I tapped in an unaligned access
when doing on the host side a "lsusb -d [vendornr]: -v"
I get on the board:

GADGET DRIVER: usb_dnl_dfu
data abort

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

pc : [<8ff71db8>]          lr : [<8ff75aec>]
sp : 8ef40d18  ip : 00000005     fp : 00000000
r10: 00000000  r9 : 47401410     r8 : 8ef40f38
r7 : 8ef4aae8  r6 : 0000000a     r5 : 8ef4ab28  r4 : 8ef4ab80
r3 : 0000000a  r2 : 00000006     r1 : 00000006  r0 : 8ef4aae8
Flags: Nzcv  IRQs off  FIQs on  Mode SVC_32
Resetting CPU ...

reason is that in the "struct usb_composite_dev" the
"struct usb_device_descriptor desc;" is on an odd address,
and this struct gets accessed in
drivers/usb/gadget/composite.c device_qual()

Fix it, by align this var "struct desc" fix to an aligned
address.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Samuel Egli <samuel.egli@siemens.com>