[MIPS] Correct HAL2 Kconfig description

The current HAL2 Kconfig description indicates it is only used on SGI
Indy systems, however all members of the Indigo2 Family have this sound
card as well.  Plus a minor grammatical fix is included.
Signed-off-by: NJoshua Kinard <kumba@gentoo.org>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

sound/oss/Kconfig

@@ -98,8 +98,8 @@ config SOUND_HAL2
 	tristate "SGI HAL2 sound (EXPERIMENTAL)"
 	depends on SOUND_PRIME && SGI_IP22 && EXPERIMENTAL
 	help
-	  Say Y or M if you have an SGI Indy system and want to be able to
-	  use it's on-board A2 audio system.
+	  Say Y or M if you have an SGI Indy or Indigo2 system and want to be able to
+	  use its on-board A2 audio system.
 
 config SOUND_IT8172
 	tristate "IT8172G Sound"