drm/xe/tests: Wait for clear fence operation to complete

Ensure the clear operation completes before proceeding, as the clear
fence is not attached to the BO's dma-resv object.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241205114702.1963303-1-nirmoy.das@intel.com


Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>