drm/xe/vm: Use xe_vm_lock()/xe_vm_unlock() helpers

drm/xe/vm: Use xe_vm_lock()/xe_vm_unlock() helpers

There is no change in functionality. Using the helper function
defined within the driver.

-v2
Use xe_vm_unlock() (Ashutosh/Matt)

-v3
Use xe_vm_unlock() for error label too (Matt)

Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@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/20240424043910.2190376-2-himal.prasad.ghimiray@intel.com