Fix this warning:

xkbActions.c: In function ‘_XkbFilterDeviceBtn’:
xkbActions.c:1084:6: warning: declaration of ‘button’ shadows a previous local [-Wshadow=compatible-local]
  int button;
      ^~~~~~
xkbActions.c:1044:6: note: shadowed declaration is here
 int  button;
      ^~~~~~

Backport of this xorg-xserver upstream commit:

  commit 41dd7cf673e47ab74c5065b8dbf268b2e5facb64
  Author: Alan Coopersmith <alan.coopersmith@oracle.com>
  Date:   Mon Dec 12 16:49:34 2011 -0800

    _XkbFilterDeviceBtn: move variable declarations to match usage scope

    The main body of this function is an if { } else if { } pair of blocks.
    Previously there was int button at the top level scope which is used
    only in the first block, and a redeclaration of int button inside the
    second block.   Since there's no overlap in the code paths for the
    two uses of button, move the one from the outer block into the first
    block to help the programmer more quickly determine they are unrelated
    usages, and to silence the gcc warning of:

    xkbActions.c: In function '_XkbFilterDeviceBtn':
    xkbActions.c:999:6: warning: declaration of 'button' shadows a previous local
    xkbActions.c:955:6: warning: shadowed declaration is here

    For consistency, move DeviceIntPtr dev declarations as well that are
    used in the same way.
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Jamey Sharp <jamey@minilop.net>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>