USB: pwc : do not pass stack allocated buffers to USB core.

This is causes problems on platforms that have alignment requirements
for DMA transfers.

Signed-off-by: Martin Fuzzey <mfuzzey@gmail.com>
Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>