parisc: also set iaoq_b in instruction_pointer_set()

When setting the instruction pointer on PA-RISC we also need
to set the back of the instruction queue to the new offset, otherwise
we will execute on instruction from the new location, and jumping
back to the old location stored in iaoq_b.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>
Fixes: 75ebedf1 ("parisc: Add HAVE_REGS_AND_STACK_ACCESS_API feature")
Cc: stable@vger.kernel.org # 4.19+