net: davicom: Use platform_get_irq_optional()

[ Upstream commit 2e269622

 ]

The second IRQ line really is optional, so use
platform_get_irq_optional() to obtain it.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>