mfd: htc-i2cpld: Fix an IS_ERR() vs NULL bug in htcpld_core_probe()

The gpiochip_request_own_desc() function returns error pointers on error,
it doesn't return NULL.

Fixes: 0ef5164a81fbf ("mfd/omap1: htc-i2cpld: Convert to a pure GPIO driver")
Signed-off-by: Peng Wu <wupeng58@huawei.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220913071659.94677-1-wupeng58@huawei.com