bus: arm-integrator-lm: Fix return value check in integrator_ap_lm_probe()

bus: arm-integrator-lm: Fix return value check in integrator_ap_lm_probe()

In case of error, the function of_find_matching_node() returns NULL
pointer not ERR_PTR(). The IS_ERR() test in the return value check
should be replaced with NULL test.

Link: https://lore.kernel.org/r/20200525091634.8274-1-linus.walleij@linaro.org
Fixes: ccea5e8a5918 ("bus: Add driver for Integrator/AP logic modules")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20200520032150.165388-1-weiyongjun1@huawei.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>