drm/amd/display: fix spelling mistake "alidation" -> "validation"

There is a spelling mistake in a DC_LOG_WARNING message. Fix it.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>