Fixed the stride size in the spinor fields
in staggered dslash. The stride in direction "i"
is nFace*ghostFace[i].
The ordering scheme in the
ghost region is
spinor_array[direction (X, Y, Z, T) ] [from -/+ direction] [color index (0,1,2)] [face_index ( 0 to nFace-1) ] [site index on face]