Staging: lustre: lproc_osc: Change the variable to be checked

The variable rc is supposed to hold the value returned by function
kstrtoul which can either be 0, -EINVAL (-22) or -ERANGE (-34).
Therefore, the check must be performed on rc instead of val for error
values. Also, rc can never be greater than 0.

Signed-off-by: Shivani Bhardwaj <shivanib134@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>