platform/x86: acer-wmi: Switch to acpi_dev_get_first_match_dev()

The acpi_dev_get_first_match_dev() helper will find and return
an ACPI device pointer of the first registered device in the system
by its HID.

Use it instead of open coded variant.

Cc: Chun-Yi Lee <jlee@suse.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>