dmaengine: pl330: Remove non-NULL check for pl330_submit_req parameters

The pl330_submit_req() checked supplied 'struct pl330_thread thrd' and
'struct dma_pl330_desc desc' parameters for non-NULL. However these
checks are useless because supplied arguments won't be NULL.

The pl330_submit_req() is called in only one place and:
1. 'desc' is already dereferenced in fill_queue() before calling
   pl330_submit_req().
2. 'thrd' is always dereferenced after calling
   fill_queue()->pl330_submit_req().

Removing the checks for non-NULL values fixes following warning:
drivers/dma/pl330.c:1376 pl330_submit_req() warn: variable dereferenced before check 'thrd' (see line 1367)

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>