can: c_can_platform: fix irq check in probe

This patch fixes the check in the probe function whether a IRQ was supplied
to the driver. The original driver check the irq "struct resource *" against
<= 0. Use "platform_get_irq" instead.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: Bhupesh Sharma <bhupesh.sharma@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>