media: staging: atomisp: Remove unnecessary return statement in void function

Return statement at the end of a void function is useless.

The Coccinelle semantic patch used to make this change is as follows:
//<smpl>
@@
identifier f;
expression e;
@@
void f(...) {
<...
- return
  e;
  ...>
  }
//</smpl>
Signed-off-by: Amitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/staging/media/atomisp/pci/atomisp2/hmm/hmm.c

@@ -640,7 +640,7 @@ void hmm_vunmap(ia_css_ptr virt)
 		return;
 	}
 
-	return hmm_bo_vunmap(bo);
+	hmm_bo_vunmap(bo);
 }
 
 int hmm_pool_register(unsigned int pool_size,