MIPS: dma-default: Defend against NULL dev in massage_gfp_flags

MIPS: dma-default: Defend against NULL dev in massage_gfp_flags

This patch ensures that the dev parameter is checked for NULL before it
is dereferenced in massage_gfp_flags. If dev is NULL, then fall back
setting the GFP flag requested and available.

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11919/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>