drm/xe/exec_queue: Remove duplicated code

This code section is the same as the body of
xe_exec_queue_last_fence_put_unlocked() so call the function instead and
remove duplicated code to make maintenance easier.

Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240809155156.1955925-6-francois.dugast@intel.com