remove add in pad when padding with non-zero

this is simpler before shapetracker is shared

tinygrad/tensor.py

@@ -1039,7 +1039,7 @@ def pad(self, padding:Union[Sequence[sint], Sequence[Optional[Tuple[sint, sint]]
     pX = ((0,0),)*(self.ndim - len(padding)//2) + tuple(zip(padding[-2::-2], padding[::-2])) if flat else padding
     if len(pX) != self.ndim: raise ValueError(f"padding length is improper, {padding=} {self.ndim=}")
     X, pX = self, cast(Tuple[Tuple[sint, sint]], tuple((0,0) if p is None else p for p in pX))
-    def _constant(x,px,v): return F.Pad.apply(x, arg=px) if v == 0 else F.Pad.apply(x, arg=px) + F.Pad.apply(Tensor.ones_like(x), arg=px).where(0, v)
+    def _constant(x,px,v): return F.Pad.apply(x, arg=px) if v == 0 else F.Pad.apply(Tensor.ones_like(x), arg=px).where(F.Pad.apply(x, arg=px), v)
     # early return for symbolic with positive pads (no need to max)
     if all(resolve(p >= 0) for p in flatten(pX)): return _constant(X, pX, value)
     pads, shrinks = tuple((smax(pB,0), smax(pA,0)) for pB,pA in pX), tuple((-smin(pB,0),smin(pA+s,s)) for (pB,pA),s in zip(pX, self.shape))