ACPI: osl: Remove the duplicated PREFIX for message printing

We have pr_fmt() in osl.c, so pr_err(PREFIX ...) is duplicated
and wrong, fix it by removing the PREFIX.

Also remove the using of PREFIX in WARN() and just add the plain
"ACPI: " in message to keep it unchanged.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>