ray_cs: Avoid reading past end of buffer

Using memcpy() from a buffer that is shorter than the length copied means
the destination buffer is being filled with arbitrary data from the kernel
rodata segment. In this case, the source was made longer, since it did not
match the destination structure size. Additionally removes a needless cast.

This was found with the future CONFIG_FORTIFY_SOURCE feature.

Cc: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>