sparc64: Fix not SRA'ed %o5 in 32-bit traced syscall

[ Upstream commit ab2abda6377723e0d5fbbfe5f5aa16a5523344d1 ]

(From v1 to v2: changed comment)

On the way linux_sparc_syscall32->linux_syscall_trace32->goto 2f,
register %o5 doesn't clear its second 32-bit.

Fix that.

Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
CC: David Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>