sh: of-generic: Add missing #include <asm/clock.h>

arch/sh/boards/of-generic.c:146:20: warning: no previous prototype for 'arch_init_clk_ops' [-Wmissing-prototypes]

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/942621553ed82e3331e2e91485b643892d2d08bc.1715606232.git.geert+renesas@glider.be


Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>