staging: android: ion: Remove redundant return of void function

This patch fix checkpatch.pl warning
Tested by compilation only.
Signed-off-by: Phong Tran <tranmanphong@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion.c

@@ -1057,7 +1057,6 @@ static void *ion_dma_buf_kmap(struct dma_buf *dmabuf, unsigned long offset)
 static void ion_dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long offset,
 			       void *ptr)
 {
-	return;
 }
 
 static int ion_dma_buf_begin_cpu_access(struct dma_buf *dmabuf, size_t start,

drivers/staging/android/ion/ion_carveout_heap.c

@@ -133,7 +133,6 @@ static struct sg_table *ion_carveout_heap_map_dma(struct ion_heap *heap,
 static void ion_carveout_heap_unmap_dma(struct ion_heap *heap,
 					struct ion_buffer *buffer)
 {
-	return;
 }
 
 static struct ion_heap_ops carveout_heap_ops = {

drivers/staging/android/ion/ion_chunk_heap.c

@@ -126,7 +126,6 @@ static struct sg_table *ion_chunk_heap_map_dma(struct ion_heap *heap,
 static void ion_chunk_heap_unmap_dma(struct ion_heap *heap,
 				     struct ion_buffer *buffer)
 {
-	return;
 }
 
 static struct ion_heap_ops chunk_heap_ops = {

drivers/staging/android/ion/ion_dummy_driver.c

@@ -152,7 +152,5 @@ static void __exit ion_dummy_exit(void)
 				dummy_heaps[ION_HEAP_TYPE_CHUNK].size);
 		chunk_ptr = NULL;
 	}
-
-	return;
 }
 __exitcall(ion_dummy_exit);

drivers/staging/android/ion/ion_system_heap.c

@@ -205,7 +205,6 @@ static struct sg_table *ion_system_heap_map_dma(struct ion_heap *heap,
 static void ion_system_heap_unmap_dma(struct ion_heap *heap,
 				      struct ion_buffer *buffer)
 {
-	return;
 }
 
 static int ion_system_heap_shrink(struct ion_heap *heap, gfp_t gfp_mask,