net: wget: fix implicit declaration

The compiler complains about the missing declaration of print_size():
net/wget.c:415:3: warning: implicit declaration of function ‘print_size’ [-Wimplicit-function-declaration]

Fix it.

Signed-off-by: Michael Walle <michael@walle.cc>

net/wget.c

@@ -6,6 +6,7 @@
 
 #include <command.h>
 #include <common.h>
+#include <display_options.h>
 #include <env.h>
 #include <image.h>
 #include <mapmem.h>