Fixes the following sparse warnings:

drivers/clk/shmobile/clk-sh73a0.c:57:17: warning:
 Using plain integer as NULL pointer
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

Driver for the SH73A0's clocks that are too specific to be supported by a
generic driver.
Signed-off-by: NUlrich Hecht <ulrich.hecht+renesas@gmail.com>
Acked-by: NMike Turquette <mturquette@linaro.org>
Tested-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>