HSI: cmt_speech: use timespec64 instead of timespec

struct timespec should no longer be used because of the y2038
overflow problem. This code does not suffer from the overflow,
but it's trivial to change it to use timespec64 without changing
the interface, so let's do that.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>