LU-12269 build: add value to definition of with_gss in spec

LU-12269 build: add value to definition of with_gss in spec

rpmbuild currently fails when gss_keyring is enabled (which
happens automatically if the right packages are installed).
This is due to an ill-formed %define in lustre.spec.in that
doesn't include the value to set the macro do.

This patch updates this line to set the value to 1.

Signed-off-by: Ben Menadue <ben.menadue@anu.edu.au>
Change-Id: I2f52b19795091702622eb3b4c110f09eb80654db
Reviewed-on: https://review.whamcloud.com/34892
Tested-by: Jenkins
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>