Based on the following commit. But for mispans.c I think the first
contained fix is wrong (nested loop with variable i) so I took another
approach.

  commit f02e27e4fcc34413b2051e5a01edc92172fa8612
  Author: Yaakov Selkowitz <yselkowitz@users.sourceforge.net>
  Date:   Tue Oct 16 02:16:17 2012 -0500

    mi: fix shadow warnings

    mibitblt.c: In function 'miGetImage':
    mibitblt.c:617:20: warning: declaration of 'pt' shadows a previous local
    mibitblt.c:609:17: warning: shadowed declaration is here
    mispans.c: In function 'miFillUniqueSpanGroup':
    mispans.c:456:33: warning: declaration of 'i' shadows a previous local
    mispans.c:382:9: warning: shadowed declaration is here
    mispans.c:488:17: warning: declaration of 'i' shadows a previous local
    mispans.c:382:9: warning: shadowed declaration is here
Signed-off-by: Yaakov Selkowitz <yselkowitz@users.sourceforge.net>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

Fixes these warnings:

mi/mispans.c: fix shadowed vars

mispans.c: In function ‘miFillUniqueSpanGroup’:
mispans.c:465:12: warning: declaration of ‘i’ shadows a previous local [-Wshadow=compatible-local]
        int i;
            ^
mispans.c:387:21: note: shadowed declaration is here
     register int    i;
                     ^
mispans.c:497:10: warning: declaration of ‘i’ shadows a previous local [-Wshadow=compatible-local]
      int i;
          ^
mispans.c:387:21: note: shadowed declaration is here
     register int    i;
                     ^

mibitblt.c: In function ‘miGetImage’:
mibitblt.c:669:13: warning: declaration of ‘pt’ shadows a previous local [-Wshadow=compatible-local]
      xPoint pt;
             ^~
mibitblt.c:659:18: note: shadowed declaration is here
     DDXPointRec  pt = {0, 0};
                  ^~