ALSA: hda: intel-sdw-acpi: Use u8 type for link index

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.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>