staging: ks7010: fix memcmp() bug

Call site to memcmp() treats return value as if it were an error code,
it is not. If memcmp() finds inputs to be not the same, an error
return code should be set explicitly.

Correctly handle return value from call to memcmp(), set error code
explicitly.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>