sparc32: signal: Fix stack trampoline for RT signals

sparc32: signal: Fix stack trampoline for RT signals

The stack trampoline generated by the sparc32 native version of
setup_rt_frame() calls sigreturn(), not rt_sigreturn().  This will
crash the task if it's ever used.  (glibc sets its own restorer, so
was not affected.)

The sparc64 compat implementation has the right syscall number.

This is untested; I have no way to run a sparc32 kernel.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>