dma-mapping: don't trace the DMA address when the allocation fails

dma_alloc_attrs() passes *dma_handle to trace_dma_alloc() without
checking whether the allocation succeeded. No backend writes it on
failure: dma_direct_alloc(), iommu_dma_alloc() and the dma_map_ops
instances assign it only on the path that returns a buffer. Callers
usually pass an uninitialized automatic variable, so a failed allocation
records whatever the stack held, next to the virt_addr=(null) that marks
the record as an error:

 dma_alloc: dmatrace dir=BIDIRECTIONAL dma_addr=deadbeefdeadbeef
 size=1099511627776 virt_addr=0000000000000000

The device coherent pool path reaches the same call: a non-zero return
from dma_alloc_from_dev_coherent() means the request was handled, not
that it succeeded, so cpu_addr is NULL and dma_handle is untouched once
the pool runs out.

For an allocation event a NULL virt_addr already means the request
failed, so the address field carries nothing. Report 0 for it in the
event class rather than at each call site, which covers dma_alloc_pages()
and dma_alloc_sgt_err() as well.

Fixes: 038eb433dc ("dma-mapping: add tracing for dma-mapping API calls")
Fixes: 68b6dbf1f4 ("dma-mapping: trace more error paths")
Suggested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
Link: https://lore.kernel.org/r/20260907120124.603373-1-donggeunyoo.kernel@gmail.com
Reviewed-by: Sean Anderson <sean.anderson@linux.dev>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

include/trace/events/dma.h

@@ -134,7 +134,7 @@ DECLARE_EVENT_CLASS(dma_alloc_class,
 	TP_fast_assign(
 		__assign_str(device);
 		__entry->virt_addr = virt_addr;
-		__entry->dma_addr = dma_addr;
+		__entry->dma_addr = virt_addr ? dma_addr : 0;
 		__entry->size = size;
 		__entry->flags = flags;
 		__entry->dir = dir;