net: cosa: fix error check return value of register_chrdev()

If major equal 0, register_chrdev() returns error code when it fails.
This function dynamically allocate a major and return its number on
success, so we should use "< 0" to check it instead of "!".

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Acked-By: Jan "Yenya" Kasprzak <kas@fi.muni.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>