drm/xe/pcode: fix pcode error check

On DG2 we are now getting:

[  104.456607] xe 0000:03:00.0: [drm] *ERROR* PCODE timeout, retrying with preemption disabled

Looks like we just need to invert the error check for
xe_pcode_try_request(), which returns zero on success.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>