Use consistently u8 for sdw link index. The id is limited to 4, u8 is
adequate in size to store it.

This change will also fixes the following compiler warning/error (W=1):

sound/hda/intel-sdw-acpi.c: In function ‘sdw_intel_acpi_scan’:
sound/hda/intel-sdw-acpi.c:34:35: error: ‘-subproperties’ directive output may be truncated writing 14 bytes into a region of size between 7 and 17 [-Werror=format-truncation=]
   34 |                  "mipi-sdw-link-%d-subproperties", i);
      |                                   ^~~~~~~~~~~~~~
In function ‘is_link_enabled’,
    inlined from ‘sdw_intel_scan_controller’ at sound/hda/intel-sdw-acpi.c:106:8,
    inlined from ‘sdw_intel_acpi_scan’ at sound/hda/intel-sdw-acpi.c:180:9:
sound/hda/intel-sdw-acpi.c:33:9: note: ‘snprintf’ output between 30 and 40 bytes into a destination of size 32
   33 |         snprintf(name, sizeof(name),
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   34 |                  "mipi-sdw-link-%d-subproperties", i);
      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

The warnings got brought to light by a recent patch upstream:
commit 6d4ab2e9 ("extrawarn: enable format and stringop overflow warnings in W=1")
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20230912162617.29178-1-peter.ujfalusi@linux.intel.comSigned-off-by: Takashi Iwai <tiwai@suse.de>