i2c: s3c2410: fix IRQ check

Iff platform_get_irq() returns 0, the driver's probe() method will return 0
early (as if the method's call was successful).  Let's consider IRQ0 valid
for simplicity -- devm_request_irq() can always override that decision...

Fixes: e0d1ec97

 ("i2c-s3c2410: Change IRQ to be plain integer.")
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>