Fixes the following W=1 kernel build warning(s):

 drivers/clk/spear/spear6xx_clock.c:116:13: warning: no previous prototype for function 'spear6xx_clk_init' [-Wmissing-prototypes]
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>