clk: spear: Add stub functions for spear3[0|1|2]0_clk_init()

clk: spear: Add stub functions for spear3[0|1|2]0_clk_init()

This fixes compile error if one of SPEAr3xx implementations is not selected.

  CC      drivers/clk/spear/spear3xx_clock.o
drivers/clk/spear/spear3xx_clock.c: In function 'spear3xx_clk_init':
drivers/clk/spear/spear3xx_clock.c:599:3: error: implicit declaration of function 'spear300_clk_init' [-Werror=implicit-function-declaration]
drivers/clk/spear/spear3xx_clock.c:601:3: error: implicit declaration of function 'spear310_clk_init' [-Werror=implicit-function-declaration]
drivers/clk/spear/spear3xx_clock.c:603:3: error: implicit declaration of function 'spear320_clk_init' [-Werror=implicit-function-declaration]
cc1: some warnings being treated as errors
make[3]: *** [drivers/clk/spear/spear3xx_clock.o] Error 1
make[2]: *** [drivers/clk/spear] Error 2
make[1]: *** [drivers/clk] Error 2
make: *** [drivers] Error 2

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>