Bluetooth: ath3k: don't use stack memory for DMA

Memory allocated by vmalloc (including stack) can not be used for DMA,
i.e. data pointer on usb_control_msg() should not point to stack memory.

Resolves:
https://bugzilla.redhat.com/show_bug.cgi?id=977558



Reported-and-tested-by: Andy Lawrence <dr.diesel@gmail.com>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>