board/evb64260/evb64260.c: Fix GC 4.6 build warning

Fix:
evb64260.c: In function 'debug_led':
evb64260.c:363:6: warning: variable 'dummy' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>