drm/radeon/dpm: fix typo in vddci setup for eg/btc

We were using the vddc mask rather than the vddci mask.

Bug:
https://bugzilla.kernel.org/show_bug.cgi?id=79071

Possibly also fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=68571



Noticed-by: Jonathan Howard <jonathan@unbiased.name>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org