dma: dma_mcux_lpc: fix scatter/gather src/dst increment

The logic for setting the src_inc and dst_inc would improperly set
these to zero when gatter/scatter was enabled but the respective
gatther_interval/scatter_interval was zero (which would imply
continuous operation).

Fixes: #85403

Signed-off-by: David Leach <david.leach@nxp.com>