Fix the incorrect mb_intra_struct for multi-slice on Haswell

Fix the incorrect mb_intra_struct for multi-slice on Haswell

Now the incorrect macroblock intra struct is passed under the multi-slice
scenario, which causes the wrong intra prediction for some macroblocks.
At the same time it also consider the scenario that the x coordinate
of the first macroblock in slice is not zero.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>