media: gp8psk: don't abuse of GFP_DMA

There's s no reason why it should be using GFP_DMA there.
This is an USB driver. Any restriction should be, instead,
at HCI core, if any.

Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: linux-mm@kvack.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>