i.MX IPU DMA: Fix wrong burstsize settings

The burstsize (npb in struct chan_param_mem) is set in
ipu_ch_param_set_size() once. The number of allowed
pixels in a burst depend on the pixel format and the
rotation mode. For 16bit formats 16 pixels are allowed
whereas for 32bit formats only 8 pixels are allowed.
Set these values correctly in ipu_ch_param_set_size()
and do not overwrite them afterwards.
We do not support rotation right now, so ignore this
case.
This patch fixes the wrong burstsize setting of 16 pixels
for 32bpp.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>