ARM: 8073/1: unwind: Use arm_get_current_stackframe

Make the unwind code use the correct API so that the frame pointer
is extracted from the correct register.

Signed-off-by: Nikolay Borisov <Nikolay.Borisov@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>