msm_fb:display: correct bus bw for downscale case

The check condition for updating bus bandwidth if downscaling is
needed was always FALSE.

Change-Id: Iec0a4d13c7737d86976d76e0dfd3ec45062799fd
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>