Input: twl4030_keypad - fix handling of platform_get_irq() error

platform_get_irq() returns -ERRNO on error.  In such case casting to
unsigned and comparing to 0 would pass the check.

Fixes: 7abf38d6 ("Input: twl4030-keypad - add device tree support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200828145744.3636-3-krzk@kernel.org


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>