drm/edid: Deletion of an unnecessary check before the function call "release_firmware"

The release_firmware() function tests whether its argument is NULL and then
returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>