sparc32: Fix inverted invalid_frame_pointer checks on sigreturns

[ Upstream commit 07b5ab3f ]

Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>