ACPICA: Hardware: Cast GPE enable_mask before storing

ACPICA commit 490ec7f7839bf7ee5e8710a34d1d1a78d54a49b6

In function acpi_hw_low_set_gpe(), cast enable_mask to u8 before
storing. The mask was read from a 32 bit register but is an 8 bit
value. Fixes Visual Studio compiler warning.

Link: https://github.com/acpica/acpica/commit/490ec7f7


Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>