ACPICA: Work around an ancient GCC bug.

warning: cast from function call of type 'char *' to non-matching type 'long unsigned int'

Since acpi_ut_format_number() hasn't been enabled for the Linux kernel,
this patch doesn't affect the Linux kernel.

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>