gfs2: remove dead code in add_to_queue

clang static analyzer complains that value stored to 'gh' is never read.
The code of this line is useless after commit 0b93bac2
("gfs2: Remove LM_FLAG_PRIORITY flag"). Remove this code to save space.

Signed-off-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>