sh: sh7723.h: bugfix: remove unused clock index

Current sh clocks are using pm_runtime frame work instead of old hwblk.
So, HWBLK_UNKNOWN, HWBLK_DBG and HWBLK_SUBC are not needed for now.

Now mstp32 clocks are registered by sh_clk_mstp32_register(),
but the clock which isn't defined by SH_CLK_MSTP32() macro
will be crash. because it doesn't have enable_reg.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>