drm/shmem-helper: Remove errant put in error path

drm_gem_shmem_mmap() doesn't own this reference, resulting in the GEM
object getting prematurely freed leading to a later use-after-free.

Link: https://syzkaller.appspot.com/bug?extid=c8ae65286134dd1b800d
Reported-by: [email protected]
Fixes: 2194a63 ("drm: Add library for shmem backed GEM objects")
Cc: [email protected]
Signed-off-by: Rob Clark <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
Signed-off-by: Javier Martinez Canillas <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: robclark

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -622,10 +622,8 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
 	}
 
 	ret = drm_gem_shmem_get_pages(shmem);
-	if (ret) {
-		drm_gem_vm_close(vma);
+	if (ret)
 		return ret;
-	}
 
 	vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);