don't open-code file_inode()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c
index 3cb5e90..2636f61 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c
@@ -283,7 +283,7 @@ void amdgpu_ring_fini(struct amdgpu_ring *ring)
 static ssize_t amdgpu_debugfs_ring_read(struct file *f, char __user *buf,
 					size_t size, loff_t *pos)
 {
-	struct amdgpu_ring *ring = (struct amdgpu_ring*)f->f_inode->i_private;
+	struct amdgpu_ring *ring = file_inode(f)->i_private;
 	int r, i;
 	uint32_t value, result, early[3];