msm: smd: Return standard error code macro

Current kernel coding conventions prefer standard error code macros be
used as return values for error conditions.  smd_packet_write() does not
conform to this convention in all scenarios.

Correct smd_packet_write() to conform to this convention in all scenarios.

Change-Id: I6e58abe2e16d7f425df5623b8ea1e7202a0c6d3d
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>