drm/xe/hw_engine_group: Fix double write lock release in error path

drm/xe/hw_engine_group: Fix double write lock release in error path

In xe_hw_engine_group_get_mode(), a write lock is acquired before
calling switch_mode(), which in turn invokes
xe_hw_engine_group_suspend_faulting_lr_jobs().

On failure inside xe_hw_engine_group_suspend_faulting_lr_jobs(),
the write lock is released there, and then again in
xe_hw_engine_group_get_mode(), leading to a double release.

Fix this by keeping both acquire and release operation in
xe_hw_engine_group_get_mode().

Fixes: 770bd1d34113 ("drm/xe/hw_engine_group: Ensure safe transition between execution modes")
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Link: https://lore.kernel.org/r/20250925023145.1203004-2-shuicheng.lin@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>