msm: mdss: Fix overriding of rgb swap parameter

Fix overriding of rgb_swap parameter in dsi driver,
as this should be read and set from panel dtsi file.

Change-Id: I1ed35f0dc4ce623ebcf3bc8e563a9d10d34a4a70
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>