habanalabs: zero complex structures using memset

fix the following sparse warnings:
'warning: Using plain integer as NULL pointer'
'warning: missing braces around initializer'

Signed-off-by: Koby Elbaz <kelbaz@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>