dmaenegine: edma: fix sparse warnings

this patch fixes following sparse warnings:

edma.c:537:32: warning: symbol 'edma_prep_dma_memcpy' was not declared. Should it be static?
edma.c:1070:6: warning: symbol 'edma_filter_fn' was not declared. Should it be static?

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>