linux/err.h isn't implicitly included by the current headers on all
platforms, resulting in compilation failures due to implicit
declarations of IS_ERR and PTR_ERR. Fix this by including linux/err.h.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>