xtensa: Don't reimplement force_sigsegv()

xtensa: Don't reimplement force_sigsegv()

Instead of open coding the sequence from force_sigsegv() just call
it. This also fixes a bug because we were modifying ka->sa.sa_handler
(which is a copy of sighand->action[]), whereas the intention of the
code was to modify sighand->action[] directly.

As the original code was working with a copy it had no effect on
signal delivery.

Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Chris Zankel <chris@zankel.net>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>