drm/msm/dsi-staging: correct return value of dsi_host_transfer

Fix the dsi_host_transfer API to accurately return the error
code in case of failures.

CRs-Fixed: 2191069
Change-Id: I54503ca2f2fc02bf2374abae5147b8c1f13eff02
Signed-off-by: Vara Reddy <varar@codeaurora.org>