drm/xe/lrc: Fix uninitialized new_ts when capturing context timestamp

drm/xe/lrc: Fix uninitialized new_ts when capturing context timestamp

Getting engine specific CTX TIMESTAMP register can fail. In that case,
if the context is active, new_ts is uninitialized. Fix that case by
initializing new_ts to the last value that was sampled in SW -
lrc->ctx_timestamp.

Flagged by static analysis.

v2: Fix new_ts initialization (Ashutosh)

Fixes: bb63e7257e63 ("drm/xe: Avoid toggling schedule state to check LRC timestamp in TDR")
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patch.msgid.link/20260312125308.3126607-2-umesh.nerlige.ramappa@intel.com
(cherry picked from commit 466e75d48038af252187855058a7a9312db9d2f8)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>