event_types_num received from the user can be 0. In that case, the
event_mask should be 0.

In addition, to create a correct mask we need to match the number
of event types to the bit location such that bit 0 represents a single
event type, bit 1 represents 2 types and so on.
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>
Reviewed-by: Ofir Bitton <obitton@habana.ai>