staging: crystalhd: fix signed bug

chd_dec_major is unsigned, so check chd_dec_major < 0 doesn't make sense.
Since it is used as signed, declare it as int.

Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>