dmaengine: dw-edma: Add pcim_iomap_table return check

Currently, is missing a null check on a pcim_iomap_table() return value
and this can lead to a null pointer dereference if the desired BAR
wasn't mapped previously.
Fix this by adding a null check and returning -ENOMEM.

Addresses-Coverity: ("Dereference null return")
Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Link: https://lore.kernel.org/r/bc5e6b8632c84660bb6dae454980e9419992ed14.1613674948.git.gustavo.pimentel@synopsys.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>