clk: hisilicon: mark wdt_mux_p[] as const

The symbol is in the __initconst section but not marked init, which
caused a warning when building with LTO.

This makes it 'const' as was obviously intended.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: c80dfd9b ("clk: hisilicon: add CRG driver for Hi3516CV300 SoC")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>