ACPI: custom_method: fix a coding style issue

Fix the following coding style issue reported by checkpatch.pl

ERROR: "foo * bar" should be "foo *bar"
FILE: drivers/acpi/custom_method.c:22:
+static ssize_t cm_write(struct file *file, const char __user * user_buf,

Signed-off-by: Xiaofei Tan <tanxiaofei@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>