memccpy: fix pointer assignment

The local vars dst and src are unsigned pointers, but two assignments
cast their value to signed explicitely.  This results in the warning
"pointer targets in assignment from ‘char *’ to ‘unsigned char *’
differ in signedness [-Wpointer-sign]" in case of -Wall.

Fix the cast.

Fixes: d254189b38 ("2002-07-23  Jeff Johnston  <jjohnstn@redhat.com>")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

newlib/libc/string/memccpy.c

@@ -118,8 +118,8 @@ memccpy (void *__restrict dst0,
         }
 
        /* Pick up any residual with a byte copier.  */
-      dst = (char*)aligned_dst;
-      src = (char*)aligned_src;
+      dst = (unsigned char*)aligned_dst;
+      src = (unsigned char*)aligned_src;
     }
 
   while (len0--)