rsi: use BUILD_BUG_ON check for fsm_state

Whenever new fsm_state enum element is added, fsm_state array
also needs to be updated. If this change is missed, we may end
up doing invalid access in array. BUILD_BUG_ON check will help
to avoid this problem.

Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>