staging: line6: Changed some strict_strtouls to kstrtou8

Adjusted strict_strtoul calls to kstrtou8 in order to take the changes of
line6_transmit_parameter() into account.

Signed-off-by: Johannes Thumshirn <morbidrsa@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>