staging: ks7010: change length type to unsigned

staging: ks7010: change length type to unsigned

Length undergoes type conversion when passed (indirectly) as an
argument for parameter of type 'unsigned int'. If length is negative
this is a bug (the value after conversion is large).

Declare 'length' to be an unsigned type instead of a signed type.

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>