memory: fsl-corenet-cf: Fix handling of platform_get_irq() error

platform_get_irq() returns -ERRNO on error.  In such case comparison
to 0 would pass the check.

Fixes: 54afbec0 ("memory: Freescale CoreNet Coherency Fabric error reporting driver")
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200827073315.29351-1-krzk@kernel.org