vnd: Fix a silly memory leak

'disp' was already allocated by LookupVendorPrivDispatch above,
clobbering it will do no good.

Signed-off-by: Adam Jackson <ajax@redhat.com>
2 jobs for glxvnd-memory-leak in 1 minute and 18 seconds
Status Name Job ID Coverage
  Docker Image
passed debian-testing #82996

00:00:14

 
  Build And Test
passed build-and-test #82997

00:01:04