pySim-prog: Replace magic numbers with a readable EF file name.

Change-Id: Ibda7d5a4132971e884f6d760baf20cd33025a2af
diff --git a/pySim-prog.py b/pySim-prog.py
index 2177d8c..44ca1fd 100755
--- a/pySim-prog.py
+++ b/pySim-prog.py
@@ -618,7 +618,7 @@
 					# Connect transport
 					print "Insert card now (or CTRL-C to cancel)"
 					sl.wait_for_card(newcardonly=not first)
-				(res,_) = scc.read_binary(['3f00', '7f20', '6f07'])
+				(res,_) = scc.read_binary(EF['IMSI'])
 				imsi = swap_nibbles(res)[3:]
 			else:
 				imsi = opts.imsi