GFS2: sparse annotation of gl->gl_spin

fs/gfs2/glock.c:308:5: warning: context problem in 'do_promote': '_spin_unlock' expected different context
fs/gfs2/glock.c:308:5:    context '*gl+28': wanted >= 1, got 0
fs/gfs2/glock.c:529:2: warning: context problem in 'do_xmote': '_spin_unlock' expected different context
fs/gfs2/glock.c:529:2:    context '*gl+28': wanted >= 1, got 0
fs/gfs2/glock.c:925:3: warning: context problem in 'add_to_queue': '_spin_unlock' expected different context
fs/gfs2/glock.c:925:3:    context '*gl+28': wanted >= 1, got 0

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>