mfd: pm8008: Fix return value check in pm8008_probe()

mfd: pm8008: Fix return value check in pm8008_probe()

In case of error, the function devm_regmap_init_i2c() returns
ERR_PTR() and never returns NULL. The NULL test in the return
value check should be replaced with IS_ERR().

Fixes: 6b149f3310a4 ("mfd: pm8008: Add driver for QCOM PM8008 PMIC")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Guru Das Srinagesh <gurus@codeaurora.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221125073626.1868229-1-yangyingliang@huawei.com