coresight: trbe: Return NULL pointer for allocation failures

When the TRBE driver fails to allocate a buffer, it currently returns
the error code "-ENOMEM". However, the caller etm_setup_aux() only
checks for a NULL pointer, so it misses the error. As a result, the
driver continues and eventually causes a kernel panic.

Fix this by returning a NULL pointer from arm_trbe_alloc_buffer() on
allocation failures. This allows that the callers can properly handle
the failure.

Fixes: 3fbf7f0 ("coresight: sink: Add TRBE driver")
Reported-by: Tamas Zsoldos <[email protected]>
Signed-off-by: Leo Yan <[email protected]>
Reviewed-by: James Clark <[email protected]>
Signed-off-by: Suzuki K Poulose <[email protected]>
Link: https://lore.kernel.org/r/20250904-cs_etm_auxsetup_fix_error_handling-v2-1-a502d0bafb95@arm.com

Author: Leo-Yan

drivers/hwtracing/coresight/coresight-trbe.c

@@ -748,12 +748,12 @@ static void *arm_trbe_alloc_buffer(struct coresight_device *csdev,
 
 	buf = kzalloc_node(sizeof(*buf), GFP_KERNEL, trbe_alloc_node(event));
 	if (!buf)
-		return ERR_PTR(-ENOMEM);
+		return NULL;
 
 	pglist = kcalloc(nr_pages, sizeof(*pglist), GFP_KERNEL);
 	if (!pglist) {
 		kfree(buf);
-		return ERR_PTR(-ENOMEM);
+		return NULL;
 	}
 
 	for (i = 0; i < nr_pages; i++)
@@ -763,7 +763,7 @@ static void *arm_trbe_alloc_buffer(struct coresight_device *csdev,
 	if (!buf->trbe_base) {
 		kfree(pglist);
 		kfree(buf);
-		return ERR_PTR(-ENOMEM);
+		return NULL;
 	}
 	buf->trbe_limit = buf->trbe_base + nr_pages * PAGE_SIZE;
 	buf->trbe_write = buf->trbe_base;