dma-sh's get_dma_error_irq() is only used by SH4, as the SH3
doesn't have the DMA Error interrupt.

Disable it out for non-SH4 builds.
Signed-off-by: NNobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>