drm/xe/guc: Accumulate CT H2G retry sleep budget

drm/xe/guc: Accumulate CT H2G retry sleep budget

guc_ct_send_wait_for_retry() introduced sleep_total_ms as a
budget guard, but never incremented it. As a result, the
"about 1 second" bailout condition never triggers in the H2G
backpressure path.

Accumulate the delay returned by xe_sleep_exponential_ms() into
sleep_total_ms so the timeout logic works as intended.

Fixes: 943c4d0637cf ("drm/xe/guc: Limit sleep while waiting for H2G credits")
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260223162350.3205364-5-shuicheng.lin@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>