sh: Fix up the address error exception handler for SH-2.

Presently the SH-2/SH-2A address error exception dispatch copies off the
register state from the stack and skips over the first register, skewing
the rest. Fix up the math here so that the proper register state is
handed down to the exception handler itself.

Signed-off-by: Kieran Bingham <kbingham@mpc-data.co.uk>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>