i2c: davinci: remove dead code in probe

From the comment of platform_get_irq, it only returns non-zero IRQ
number and negative error number, other than zero.

Fix this by removing the if condition.

Signed-off-by: Dongliang Mu <dzm91@hust.edu.cn>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>