drm/i915/display: Fix possible overflow on tc power domain selection

drm/i915/display: Fix possible overflow on tc power domain selection

There is a possibility that intel_encoder_to_tc() function
returns negative i.e. TC_PORT_NONE (-1) value which may cause
tc_port_power_domain() function to overflow. To fix this,
let's add additional check that returns invalid power domain
i.e. POWER_DOMAIN_INVALID in case tc port equals TC_PORT_NONE.

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/20250829101226.4085757-1-mika.kahola@intel.com