msm: mdss: fix the pixel clock calculation for fb modes

In the current implementation, if panel is configured in split
mode and supports multiple resolutions, then the pixel clock
calculation for the supported modes does not take split mode
into consideration. This causes issues when recovery or charger
application try to configure display. So fix the same by
recalculating the pixel clock with taking care of proper width
in case of split mode panel.

Change-Id: Ie6b50bcd67d3e283610f8b04ac0a974b3527e552
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>