drivers: dma_mcux_lpc: Fix busy status

Driver should just say the channel is not busy if
it is not setup rather than returning an error.

Also, change the channel index to int8_t rather
than uint32_t since it is being assigned negative
values and that width is more appropriate.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>
1 file changed