ARM32: Address displacement is 0 for volatile field access because of Unsafe field access.

(issue reported by christoph.goettschkes@microdoc.com)

In the LIRGenerator::volatile_field_store() and LIRGenerator::volatile_field_load(), the target address is calculated by using the function add_large_constant(), which asserts that the given displacement is not 0. But in the implementation of the intrinsic for the Unsafe class, this can actually happen.