staging: lustre: Delete an unnecessary variable initialisation in class_register_type()

The variable "rc" will be eventually set to an error return code in the
class_register_type() function.
Thus let us omit the explicit initialisation at the beginning.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>