Consistently use the reservation object wrappers instead of accessing
the ww_mutex directly.

Additional to that use the reservation object wrappers directly instead of
calling __ttm_bo_reserve with fixed parameters.

v2: fix typo
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-and-Tested-by: NMichel Dänzer <michel.daenzer@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>