staging: vt6655: wcmd.c: fix print priority warning

This patch fixes the following warning generated by checkpatch.pl
for the file wcmd.c

WARNING: printk() should include KERN_ facility level

printk was replaced by netdev_err since providing printk with the
facility level KERN_ERR generated the printing priority warning.

Signed-off-by: Aya Mahfouz <mahfouz.saif.elyazal@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>