USB: pass mem_flags to dma_alloc_coherent

When I want to use my webcam, I get:

                                 vvvvvvv
cheese: page allocation failure. order:5, mode:0x8004
Pid: 8100, comm: cheese Not tainted 2.6.30-rc2-wl-dirty #102
Call Trace:
 [<ffffffff802c5d8e>] __alloc_pages_internal+0x3fe/0x520
 [<ffffffff80210a20>] dma_generic_alloc_coherent+0x90/0x120
 [<ffffffffa001c91e>] hcd_buffer_alloc+0xee/0x130 [usbcore]
 [<ffffffffa000d52d>] usb_buffer_alloc+0x2d/0x40 [usbcore]
 [<ffffffffa0160e14>] uvc_alloc_urb_buffers+0x84/0x140 [uvcvideo]
 [<ffffffffa0160ff6>] uvc_init_video+0x126/0x400 [uvcvideo]
 [...]

Oddly, I remembered fixing this and putting in __GFP_NOWARN
because uvcvideo retries a smaller allocation. However, the
allocation function doesn't pass the gfp flags through to
dma_alloc_coherent so we still get the warning!

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>