clocksource: sh_mtu2: Tidy up Kconfig typo for MTU2

It should be "MTU2" instead of "TMU2"
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Wolfram Sang <wsa@sang-engineering.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/Kconfig

@@ -175,7 +175,7 @@ config SH_TIMER_MTU2
 	default SYS_SUPPORTS_SH_MTU2
 	help
 	  This enables build of a clockevent driver for the Multi-Function
-	  Timer Pulse Unit 2 (TMU2) hardware available on SoCs from Renesas.
+	  Timer Pulse Unit 2 (MTU2) hardware available on SoCs from Renesas.
 	  This hardware comes with 16 bit-timer registers.
 
 config SH_TIMER_TMU