drm/i915/guc: Replace check for golden context size

drm/i915/guc: Replace check for golden context size

In the other places in this function, guc->ads_map is being protected
from access when it's not yet set. However the last check is actually
about guc->ads_golden_ctxt_size been set before.  These checks should
always match as the size is initialized on the first call to
guc_prep_golden_context(), but it's clearer if we have a single return
and check for guc->ads_golden_ctxt_size.

This is just a readability improvement, no change in behavior.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220216174147.3073235-12-lucas.demarchi@intel.com