dma-buf: heaps: system: Remove global variable

The system heap is storing its struct dma_heap pointer in a global
variable but isn't using it anywhere.

Let's move the global variable into system_heap_create() to make it
local.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250407-dma-buf-ecc-heap-v3-1-97cdd36a5f29@kernel.org
Signed-off-by: Christian König <christian.koenig@amd.com>

Author: mripard

drivers/dma-buf/heaps/system_heap.c

@@ -21,8 +21,6 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 
-static struct dma_heap *sys_heap;
-
 struct system_heap_buffer {
 	struct dma_heap *heap;
 	struct list_head attachments;
@@ -424,6 +422,7 @@ static const struct dma_heap_ops system_heap_ops = {
 static int __init system_heap_create(void)
 {
 	struct dma_heap_export_info exp_info;
+	struct dma_heap *sys_heap;
 
 	exp_info.name = "system";
 	exp_info.ops = &system_heap_ops;