drm/radeon: adjust tested variable

Check the variable that was most recently initialized.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/

)

// <smpl>
@@
expression x, y, f, g, e, m;
statement S1,S2,S3,S4;
@@

x = f(...);
if (\(<+...x...+>\&e\)) S1 else S2
(
x = g(...);
|
m = g(...,&x,...);
|
y = g(...);
*if (e)
 S3 else S4
)
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org