staging: ks7010: remove custom return values

Driver code uses custom return values (often positive) to signal error
condition instead of using standard kernel error codes.

Replace custom return values with standard kernel error codes.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>