ARM64 / ACPI: fix usage of acpi_map_gic_cpu_interface

acpi_parse_gic_cpu_interface calls acpi_map_gic_cpu_interface by both
passing a 32-bit value in the u8 enabled parameter and then subsequently
ignoring its return value.

Sort it out.

Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>