ALSA: riptide: Properly endian notations

The SG descriptor of Riptide contains the little-endian values, hence
we need to define with __le32 properly.  This fixes sparse warnings
like:
  sound/pci/riptide/riptide.c:1112:40: warning: cast to restricted __le32
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/riptide/riptide.c

@@ -470,10 +470,10 @@ struct snd_riptide {
 };
 
 struct sgd {			/* scatter gather desriptor */
-	u32 dwNextLink;
-	u32 dwSegPtrPhys;
-	u32 dwSegLen;
-	u32 dwStat_Ctl;
+	__le32 dwNextLink;
+	__le32 dwSegPtrPhys;
+	__le32 dwSegLen;
+	__le32 dwStat_Ctl;
 };
 
 struct pcmhw {			/* pcm descriptor */