gpu: host1x: Fix offset calculation in trace_write_gather

When a gather longer than 2*TRACE_MAX_LENGTH (256) words is traced
through host1x_cdma_push_gather, the reported BO offset drifts from
the third iteration onward.

Fix the calculation by properly calculating the value on each loop
rather than accumulating.

In reality, gathers tend to be pretty short so this is unlikely to
ever have been observed.

Fixes: b40d02bf96 ("gpu: host1x: Use struct host1x_bo pointers in traces")
Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patch.msgid.link/20260609-b4-host1x-small-fixes-a-v1-3-7c1131c0b3ad@nvidia.com

drivers/gpu/host1x/hw/channel_hw.c

@@ -36,10 +36,9 @@ static void trace_write_gather(struct host1x_cdma *cdma, struct host1x_bo *bo,
 		for (i = 0; i < words; i += TRACE_MAX_LENGTH) {
 			u32 num_words = min(words - i, TRACE_MAX_LENGTH);
 
-			offset += i * sizeof(u32);
-
 			trace_host1x_cdma_push_gather(dev_name(dev), bo,
-						      num_words, offset,
+						      num_words,
+						      offset + i * sizeof(u32),
 						      mem);
 		}