Initialize prev_intr_delay_resolution with ena_dev->intr_delay_resolution
unconditionally, since it is initialized with
ENA_DEFAULT_INTR_DELAY_RESOLUTION in ena_probe(). This approach makes much
more sense than handling errors of not initializing it.

Also added unlikely to if condition.
Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>