staging: android: ion: Return an ERR_PTR in ion_map_kernel

The expected return value from ion_map_kernel is an ERR_PTR. The error
path for a vmalloc failure currently just returns NULL, triggering
a warning in ion_buffer_kmap_get. Encode the vmalloc failure as an ERR_PTR.

Reported-by: syzbot+55b1d9f811650de944c6@syzkaller.appspotmail.com
Signed-off-by: Laura Abbott <labbott@redhat.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion_heap.c

@@ -30,7 +30,7 @@ void *ion_heap_map_kernel(struct ion_heap *heap,
 	struct page **tmp = pages;
 
 	if (!pages)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	if (buffer->flags & ION_FLAG_CACHED)
 		pgprot = PAGE_KERNEL;