ARM: shmobile: r8a7793: proper constness with __initconst

Both the pointer array and the pointed data have to be const when using
__initconst to be correct.  This also fixes LTO builds that otherwise
fail with section mismatch errors.

Fixes: ec60d95b ("ARM: shmobile: Basic r8a7793 SoC support")
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>