msm: mdss: match pixclock calculation for videomode and fb var

When multiple panel timings are available and enumerating videomode
list, pixclock is calculated using htotal, vtotal and refresh rate.
But fb var struct is populated with actual pixclock value calculated
by DSI. This pixclock mismatch would cause issues, when usermode
does GET_VSCREENINFO/PUT_VSCREENINFO. Fix by using the same pixclock
calculation for both structures.

Change-Id: I42bfc40b5904ec80f20b296e3b4610ca3b2c5ee0
[veeras@codeaurora.org: Resolved conflicts in mdss_fb.c]
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>