drm/xe/guc: Do not assert CTB state while sending MMIO

During VF post-migration recovery, MMIO communication channel to GuC
is used, despite CTB channel being enabled. This behavior is rooted
in the save-restore architecture specification.

Therefore, a VF driver cannot assert that CTB is disabled while sending
MMIO messages to GuC. Such assertion needs to be PF only, or be removed.

This patch simply removes the assertion.

Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Suggested-by: Michał Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241107151357.1623733-2-tomasz.lis@intel.com