keucr: migrate printk to dev_dbg/info/warn/err

as per suggestion of checkpatch.pl; this resolves warnings like "Prefer
netdev_info .. then dev_info .. to printk".
Changed signature of function usb_stor_print_cmd in init.c to enable
usage of dev_err

Signed-off-by: Laura Lawniczak <laura.lawniczak@googlemail.com>
Signed-off-by: Johannes Schilling <of82ecuq@cip.cs.fau.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>