Input: melfas_mip4 - fix return value check in mip4_probe()

[ Upstream commit a54dc27b ]

devm_gpiod_get_optional() may return ERR_PTR(-EPROBE_DEFER),
add a minus sign to fix it.

Fixes: 6ccb1d8f

 ("Input: add MELFAS MIP4 Touchscreen driver")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220924030715.1653538-1-yangyingliang@huawei.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>