msm_fb: display: set pipe src and dst size same in solid fill mode

When a mdp pipe is in solid fill mode, the pipe outputs constant color
and pipe itself does not fetch data from memory, so pipe src size
should not matter. However, when src size is greater than dst size in
solid mode which means downscaling, underrun happens. In this
situation, setting src size to be same as dst size can remove underrun.

CRs-fixed: 368478
Change-Id: Ie3ffc34486129cddcc872fe6e5317873db985b97
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>