[ALSA] Fix description of ALSA/OSS device mapping

Documentation
Fixed the description of ALSA/OSS device mapping.  The direction
suffix was missing in ALSA devices.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/alsa/ALSA-Configuration.txt

@@ -1402,18 +1402,21 @@ In this example, the interwave card is always loaded as the first card
 ALSA PCM devices to OSS devices mapping
 =======================================
 
-/dev/snd/pcmC0D0  -> /dev/audio0 (/dev/audio) -> minor 4
-/dev/snd/pcmC0D0  -> /dev/dsp0 (/dev/dsp)     -> minor 3
-/dev/snd/pcmC0D1  -> /dev/adsp0 (/dev/adsp)   -> minor 12
-/dev/snd/pcmC1D0  -> /dev/audio1              -> minor 4+16 = 20
-/dev/snd/pcmC1D0  -> /dev/dsp1                -> minor 3+16 = 19
-/dev/snd/pcmC1D1  -> /dev/adsp1               -> minor 12+16 = 28
-/dev/snd/pcmC2D0  -> /dev/audio2              -> minor 4+32 = 36
-/dev/snd/pcmC2D0  -> /dev/dsp2                -> minor 3+32 = 39
-/dev/snd/pcmC2D1  -> /dev/adsp2               -> minor 12+32 = 44
-
-The first number from /dev/snd/pcmC{X}D{Y} expression means soundcard number
-and second means device number.
+/dev/snd/pcmC0D0[c|p]  -> /dev/audio0 (/dev/audio) -> minor 4
+/dev/snd/pcmC0D0[c|p]  -> /dev/dsp0 (/dev/dsp)     -> minor 3
+/dev/snd/pcmC0D1[c|p]  -> /dev/adsp0 (/dev/adsp)   -> minor 12
+/dev/snd/pcmC1D0[c|p]  -> /dev/audio1              -> minor 4+16 = 20
+/dev/snd/pcmC1D0[c|p]  -> /dev/dsp1                -> minor 3+16 = 19
+/dev/snd/pcmC1D1[c|p]  -> /dev/adsp1               -> minor 12+16 = 28
+/dev/snd/pcmC2D0[c|p]  -> /dev/audio2              -> minor 4+32 = 36
+/dev/snd/pcmC2D0[c|p]  -> /dev/dsp2                -> minor 3+32 = 39
+/dev/snd/pcmC2D1[c|p]  -> /dev/adsp2               -> minor 12+32 = 44
+
+The first number from /dev/snd/pcmC{X}D{Y}[c|p] expression means
+soundcard number and second means device number.  The ALSA devices
+have either 'c' or 'p' suffix indicating the direction, capture and
+playback, respectively.
+
 Please note that the device mapping above may be varied via the module
 options of snd-pcm-oss module.