msm_fb: display: fix underrun seen due to scaling accuracy

When making scale phase step ratio calculation, accuracy is lost when
sizes are big since calculation is done in 32 bit and some truncation
happens; this leads to underrun in mdp hw since scaling ratio doesn't
match the src/dst rectangle. Increase accuracy by performing division
again on remainder and appending to lsb of ratio.

Change-Id: I6baa69a70a55e402c8924b51cab86afa6d0e9b5c
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>