net: Add prototype for update_tftp

This function should be declared in net.h.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/common/cmd_fitupd.c b/common/cmd_fitupd.c
index 7a3789e..618ff7c 100644
--- a/common/cmd_fitupd.c
+++ b/common/cmd_fitupd.c
@@ -8,13 +8,12 @@
 
 #include <common.h>
 #include <command.h>
+#include <net.h>
 
 #if !defined(CONFIG_UPDATE_TFTP)
 #error "CONFIG_UPDATE_TFTP required"
 #endif
 
-extern int update_tftp(ulong addr);
-
 static int do_fitupd(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	ulong addr = 0UL;