gpu: host1x: Make gather offsets unsigned

Use the u32 type for the offset in the host1x_job_gather structure for
consistentcy with other structures. Negative offsets don't make sense in
this context.

Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/host1x/job.h

···
 	u32 words;
 	dma_addr_t base;
 	struct host1x_bo *bo;
-	int offset;
+	u32 offset;
 	bool handled;
 };