niu: Fix error checking in niu_ethflow_to_class.
niu: Fix error checking in niu_ethflow_to_class.

The callers of niu_ethflow_to_class expect zero as error, but it returns
-1 instead.

Signed-off-by: Andreas Schwab <c9df6394cb541f693236245820fbe23866f1a3fe@suse.de>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs