drm/i915/display: Do not check for the ddb allocations of turned off pipes

It should not care about DDB allocations of pipes going through
a fullmodeset, as at this point those pipes are disabled.
The comment in the code also points to that but that was not what
was being executed.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191205210350.96795-1-jose.souza@intel.com