clk/efm32gg: fix dt init prototype

clk/efm32gg: fix dt init prototype

Since commit 54196ccbe0ba (of: consolidate linker section OF match table
declarations) which went into 3.16-rc1 the following compiler warning is
generated:

	In file included from drivers/clk/clk-efm32gg.c:12:0: include/linux/of.h:772:20:
	warning: comparison of distinct pointer types lacks a cast [enabled by default]
		.data = (fn == (fn_type)NULL) ? fn : fn  }
			    ^
	include/linux/of.h:785:3: note: in expansion of macro '_OF_DECLARE'
	   _OF_DECLARE(table, name, compat, fn, of_init_fn_1)
	   ^
	include/linux/clk-provider.h:545:42: note: in expansion of macro 'OF_DECLARE_1'
	 #define CLK_OF_DECLARE(name, compat, fn) OF_DECLARE_1(clk, name, compat, fn)
						  ^
	drivers/clk/clk-efm32gg.c:81:1: note: in expansion of macro 'CLK_OF_DECLARE'
	 CLK_OF_DECLARE(efm32ggcmu, "efm32gg,cmu", efm32gg_cmu_init);
	 ^

Fix it by making efm32gg_cmu_init return void.

Cc: Rob Herring <robh@kernel.org>
Reported-by: Bryan Hundven <bryanhundven@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Mike Turquette <mturquette@linaro.org>