inc_curr_1vb_split: use inv

Author: JamesMcClung

src/libpsc/psc_push_particles/inc_curr_1vb_split.cxx

@@ -15,7 +15,7 @@ struct Current1vbSplit
 
   Current1vbSplit(const Grid_t& grid)
     : dt_(grid.dt),
-      dxi_{Real3{1., 1., 1.} / Real3(grid.domain.dx)},
+      dxi_{grid.domain.dx.inv()},
       deposition_(real_t(grid.norm.fnqs / grid.dt) * Real3(grid.domain.dx))
   {}