drivers: dma: pl330: Zero initialize the ch_handle

Zero initialize the ch_handle in dma_pl330_configure().
The memset in dma_pl330_config_channel()is incorrect,
as the ch_handle is already populated with valid values and
the dma_pl330_config_channel() is overwriting with zeros.

Signed-off-by: Arjun Jyothi <arjun.jyothi@broadcom.com>