m32r: build fix for processors without ISA_DSP_LEVEL2

Additional fixes for processors without ISA_DSP_LEVEL2.  sigcontext_t does not
have dummy_acc1h, dummy_acc1l members any longer.

Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>