msm: mdss: fix for black stripe flicker in browse scroll

Fix a typo that was comparing the width instead of the height
parameter that lead to black stripe flickering when scrolling on
browser.

Change-Id: I10e57f876458f46d445b3404d09a5e7606aeb666
Signed-off-by: Vinu Deokaran <vinud@codeaurora.org>