msm: sde: change error checking of return value on dma map ops

Changes the error checking when calling dma mapping operations.
The number of address segments mapped by dma_map_sg may be shorter
than the requested number of entries if the iova in the lists are
adjacent.  Therefore it is possible for mismatches between the
return value and the expected number of entries.  To test for
successful mapping, all that is required is to check that a
non-zero value was returned.

Change-Id: I4d5e2e4eecc64f314515247b49939402ee3d924c
Signed-off-by: Steve Cohen <cohens@codeaurora.org>