drm/msm: Fix error path clean-up for buffer object creation

The reference count on a buffer object was being
decremented before it was initialized. Fix the
error path clean-up to put the reference only
after the kref has been initialized. Also, avoid
passing the object by reference when possible.

Change-Id: Ifbb1874deb5db9ae3fb2fbd40a58162998284e96
Signed-off-by: Sushmita Susheelendra <ssusheel@codeaurora.org>