C6X: clean up compiler warning

commit a610d6e6: pull clearing RESTORE_SIGMASK into block_sigmask()
left behind a compiler warning:

  arch/c6x/kernel/signal.c:252:6: warning: unused variable 'ret'

This patch cleans up the warning by removing the unused variable.

Signed-off-by: Mark Salter <msalter@redhat.com>