macppc: fix volume +/- from keyboard (i2s)

[Martin Pieuchot]

This diff fix the use of the volume keys +/- for the iBooks/PowerBooks.

Index: dev/i2s.c
===================================================================
RCS file: /cvs/src/sys/arch/macppc/dev/i2s.c,v
retrieving revision 1.18
diff -u -p -r1.18 i2s.c
--- dev/i2s.c   15 Jul 2010 03:43:11 -0000      1.18
+++ dev/i2s.c   3 May 2011 08:01:16 -0000
@@ -637,9 +637,7 @@ i2s_get_port(h, mc)
 }
 
 int
-i2s_query_devinfo(h, dip)
-       void *h;
-       mixer_devinfo_t *dip;
+i2s_query_devinfo(void *h, mixer_devinfo_t *dip)
 {
        struct i2s_softc *sc = h;
        int n = 0;
@@ -674,6 +672,7 @@ i2s_query_devinfo(h, dip)
                dip->type = AUDIO_MIXER_VALUE;
                dip->prev = dip->next = AUDIO_MIXER_LAST;
                dip->un.v.num_channels = 2;
+               dip->un.v.delta = 8;
                strlcpy(dip->un.v.units.name, AudioNvolume,
                    sizeof(dip->un.v.units.name));
                return 0;