drm/amd/powerplay: fix copy-n-paste error on vddci_buf index

The index to vddci_buf is using profile->ucElbVDDC_Num rather
than profile->ucElbVDDCI_Num; this looks like a copy-n-paste
error from previous code for the vddc_buf array and I'm pretty
sure this is incorrect. Fix this by using the correct variable.

Detected by CoverityScan, CID#1457172 ("Copy-paste error")

Fixes: 970d9804 ("drm/amd/powerplay: Add support functions for CI to ppatomctrl.c")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>