ACPICA: Resources: Fix loop termination for the get AML length function.

The loop terminates on a NULL resource pointer, which can never
happen since the loop simply increments a valid resource pointer.
This fix changes the loop to terminate on an end-of-buffer condition.

Problem can be seen by callers to AcpiSetCurrentResources with an
invalid or corrupted resource descriptor; or a resource descriptor
without an END_TAG descriptor.

(refined by Bob Moore)
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>