ALSA: au88x0: use explicitly signed char

With char becoming unsigned by default, and with `char` alone being
ambiguous and based on architecture, signed chars need to be marked
explicitly as such. This fixes warnings like:

sound/pci/au88x0/au88x0_core.c:2029 vortex_adb_checkinout() warn: signedness bug returning '(-22)'
sound/pci/au88x0/au88x0_core.c:2046 vortex_adb_checkinout() warn: signedness bug returning '(-12)'
sound/pci/au88x0/au88x0_core.c:2125 vortex_adb_allocroute() warn: 'vortex_adb_checkinout(vortex, (0), en, 0)' is unsigned
sound/pci/au88x0/au88x0_core.c:2170 vortex_adb_allocroute() warn: 'vortex_adb_checkinout(vortex, stream->resources, en, 4)' is unsigned

As well, since one function returns errnos, return an `int` rather than
a `signed char`.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20221024162929.536004-1-Jason@zx2c4.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/au88x0/au88x0.h

@@ -141,7 +141,7 @@ struct snd_vortex {
 #ifndef CHIP_AU8810
 	stream_t dma_wt[NR_WT];
 	wt_voice_t wt_voice[NR_WT];	/* WT register cache. */
-	char mixwt[(NR_WT / NR_WTPB) * 6];	/* WT mixin objects */
+	s8 mixwt[(NR_WT / NR_WTPB) * 6];	/* WT mixin objects */
 #endif
 
 	/* Global resources */
@@ -235,8 +235,8 @@ static int vortex_alsafmt_aspfmt(snd_pcm_format_t alsafmt, vortex_t *v);
 static void vortex_connect_default(vortex_t * vortex, int en);
 static int vortex_adb_allocroute(vortex_t * vortex, int dma, int nr_ch,
 				 int dir, int type, int subdev);
-static char vortex_adb_checkinout(vortex_t * vortex, int resmap[], int out,
-				  int restype);
+static int vortex_adb_checkinout(vortex_t * vortex, int resmap[], int out,
+				 int restype);
 #ifndef CHIP_AU8810
 static int vortex_wt_allocroute(vortex_t * vortex, int dma, int nr_ch);
 static void vortex_wt_connect(vortex_t * vortex, int en);

sound/pci/au88x0/au88x0_core.c

@@ -1998,7 +1998,7 @@ static const int resnum[VORTEX_RESOURCE_LAST] =
  out: Mean checkout if != 0. Else mean Checkin resource.
  restype: Indicates type of resource to be checked in or out.
 */
-static char
+static int
 vortex_adb_checkinout(vortex_t * vortex, int resmap[], int out, int restype)
 {
 	int i, qty = resnum[restype], resinuse = 0;