[MIPS] Fix RBTX49x7 board name

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -595,7 +595,7 @@ config TOSHIBA_JMR3927
 	select GENERIC_HARDIRQS_NO__DO_IRQ
 
 config TOSHIBA_RBTX4927
-	bool "Toshiba TBTX49[23]7 board"
+	bool "Toshiba RBTX49[23]7 board"
 	select DMA_NONCOHERENT
 	select HAS_TXX9_SERIAL
 	select HW_HAS_PCI