Fix map_sigma function (PanDDA2)

Author: rowanwalker96

src/dlstbx/wrapper/pandda_xchem.py

@@ -360,7 +360,7 @@ def read_pandda_map(self, xmap_file):
         dmap = dmap_ccp4.grid
         return dmap
 
-    def map_sigma(xmap, sigma):
+    def map_sigma(self, xmap, sigma):
         ccp4 = gemmi.read_ccp4_map(str(xmap))
         ccp4.setup(0.0)
         grid = ccp4.grid