Improved readability and simplicity of fix

Added suggestion from pull request

vispy/visuals/surface_plot.py

@@ -70,9 +70,7 @@ def _update_z_data(self, z):
         if z is not None:
             if self._x is not None and z.shape[0] != len(self._x):
                 raise TypeError('Z values must have shape (len(x), len(y))')
-            if self._y is not None and\
-                ((self._y.ndim == 1 and z.shape[1] != len(self._y)) or \
-                 (self._y.ndim == 2 and z.shape[1] != self._y.shape[1])):    
+            if self._y is not None and z.shape[1] != self._y.shape[-1]:    
                 raise TypeError('Z values must have shape (len(x), len(y)) or (x.shape[0], y.shape[1])')
             self._z = z
             if (self.__vertices is not None and