disp: msm: sde: Fix data width calculation when widebus is enabled

Adjust the data width calculation to reduce the rounding off error
when the widebus is enabled.

Change-Id: Ia2fa4536ce519548989e2befcb22fb685f286c9e
Signed-off-by: Kashish Jain <quic_kashjain@quicinc.com>