sh: Fix up thread info pointer in syscall_badsys resume path.

Entry to resume_userspace expects r8 to contain current_thread_info,
which happens in all paths except for syscall_badsys, where r8 was
being inadvertently trampled. Reload it before the branch.

Signed-off-by: Hideo Saito <saito@densan.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>