staging: lustre: make sptlrpc_flavor_has_bulk return boolean

This patch makes sptlrpc_flavor_has_bulk return boolean, since
this function only uses either one or zero as its return value.

Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>