SurfaceControl: Correct setMatrix parameter naming.

The first parameter dsdx controls the X scaling. The last parameter
is called dtdy but controls the Y scaling. Clearly this was meant to be
named dsdy. You can verify this with a quick look at Transaction_test.

Test: Tried various stuff, phone still works.
Change-Id: Ie9e898443350ffdcf227888a8d85efdbe1b6b033