Fix shadow warning:

xkbLEDs.c: In function ‘XkbFindSrvLedInfo’:
xkbLEDs.c:633:19: warning: declaration of ‘sli’ shadows a previous local [-Wshadow=compatible-local]
  XkbSrvLedInfoPtr sli;
                   ^~~
xkbLEDs.c:629:18: note: shadowed declaration is here
 XkbSrvLedInfoPtr sli;
                  ^~~

Backport of this xorg-xserver commit:

  commit d8eb9b5faa2d2c9350bdaffef8749a9cac3c87b8
  Author: Alan Coopersmith <alan.coopersmith@oracle.com>
  Date:   Mon Dec 12 16:49:34 2011 -0800

    XkbFindSrvLedInfo: remove extraneous name-clashing sli variable

    Variable is already defined outside the outer if statement, and
    there's no need to redefine inside the if statement.

    No point in setting sli before if (dev->kbdfeed->xkb_sli==NULL)
    check - if check is true, we immediately set it, if check is false,
    we immediately return without further reference or use of it.

    The one thing we do with it inside the inner if statement is store
    an allocation in it for a brief moment before writing to the final
    destination, which is immediately returned to the caller.

    In short, there's no benefit to the variable at all in this block,
    it just gives the optimizer more code to figure out how to omit.

    Fixes gcc warning:
    xkbLEDs.c: In function 'XkbFindSrvLedInfo':
    xkbLEDs.c:683:19: warning: declaration of 'sli' shadows a previous local
    xkbLEDs.c:679:18: warning: shadowed declaration is here
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>