[Ada] Fix typo in Covers_Some_Interface predicate

[Arnaud Charlet]

This patchlet eliminates a typo in Covers_Some_Interface.

Tested on x86_64-pc-linux-gnu, committed on trunk

2011-10-24  Eric Botcazou  <ebotcazou@adacore.com>

	* sem_disp.adb (Covers_Some_Interface): Fix typo.

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Index: sem_disp.adb
===================================================================
--- sem_disp.adb	(revision 180365)
+++ sem_disp.adb	(working copy)
@@ -160,7 +160,7 @@
                   while Present (Elmt) loop
                      Iface_Prim := Node (Elmt);
 
-                     if Chars (E) = Chars (Prim)
+                     if Chars (Iface) = Chars (Prim)
                        and then Is_Interface_Conformant
                                   (Tagged_Type, Iface_Prim, Prim)
                      then