target-alpha: Fix ret instruction

Hopefully pine doesn't corrupt this patch, I've had problems recently.

For an alpha "ret" instruction, of the type
     ret $26

The return was being ignored.  This is because in translate.c
register $26 (the return address) was being over-written with the current
PC before it could be jumped to.  Thus the ret was ignored.

This patch just re-orders things so the return address is processed before
it is over-written with the current PC.

(Vince Weaver)

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5638 c046a42c-6fe2-441c-8c8c-71466251a162
