msm: mdss: account for multirect when enumerating pipe formats

The pipe format enumeration is not accounting for multi-rect on the
pipe list. Update the loop enumerating formats to account for multiple
rectangles per pipe.

Change-Id: Ief1980e2888525434e876f7cec4357403ca20cb1
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>