i2c: mlxbf: Fix the return check of devm_ioremap and ioremap

devm_ioremap and ioremap may return NULL which cannot be checked
by IS_ERR.

Signed-off-by: Wang Xiaojun <wangxiaojun11@huawei.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: Khalil Blaiech <kblaiech@nvidia.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>