dmaengine: sh: rz_dmac: make error interrupt optional

dmaengine: sh: rz_dmac: make error interrupt optional

The Renesas RZ/T2H (R9A09G077) and RZ/N2H (R9A09G087) SoCs do not have
an error interrupt for the DMACs, and the current driver implementation
does not make much use of it.

To prepare for adding support for these SoCs, do not error out if the
error interrupt is missing.

Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20260105114445.878262-2-cosmin-gabriel.tanislav.xa@renesas.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>