cmd_net.c: fix build breakage

Commit 722b061b "autocomplete: remove runtime handler install" caused
some boards (like NETTA2_V2) to break with errors like these:

cmd_net.c:296: error: expected expression before ',' token

Fix this.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Mike Frysinger <vapier@gentoo.org>