mips: fixup blksys_restart address for mips64

Restart logic has changed in kernel, this is counterpart in Valgrind.

This change fixes:

none/tests/syscall-restart1
none/tests/syscall-restart2

for mips64.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13379 a5019735-40e9-0310-863c-91ae7b9d1cf9