drm/amd/pp: Fix spelling mistake: "suppported" -> "supported"

Trivial fix to spelling mistake in pr_warn warning message text

Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>