drm/i915/display: vcpi is always greater than zero

drm/i915/display: vcpi is always greater than zero

Static analysis issue:

intel_conn_to_vcpi currently checks and asserts vcpi >= 0, as grabbed
from payload->vcpi.  But payload->vcpi is a u8, so this is always true.
Remove this unnecessary check.

While we're here, the jump statements in this function are largely
defunct now, so remove those as well.

Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patch.msgid.link/20260123170914.64548-2-jonathan.cavitt@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>