dmaengine: tegra: reduce channel name field size

The name field is used for "apbdma.%d" which is rarely going to be
more than 10 bytes, so reduce the size from 30 to 12. This is only
being used by the interrupt registration, so is not critical to the
operation of the driver either.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>