frv: handling of restart into restart_syscall is fscked

do_signal() should place the syscall number in gr7, not gr8 when
handling ERESTART_WOULDBLOCK.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>