powerpc/mce: Remove unused function get_mce_fault_addr()

There are no users of get_mce_fault_addr() since commit
1363875b ("powerpc/64s: fix handling of non-synchronous machine
checks") removed the last usage.

Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>