drm/xe/rtp: Allow to match 0 sr entries

If none of the rules match, there should be 0 entries in the sr xarray,
so none of them should have a register matching.

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240618050044.324454-2-lucas.demarchi@intel.com