GFS2: fix DLM depends to fix build errors

Fix build errors by correcting DLM dependencies in GFS2.
Build errors happen when CONFIG_GFS2_FS_LOCKING_DLM=y and CONFIG_DLM=m:

fs/built-in.o: In function `gfs2_lock':
file.c:(.text+0xc7abd): undefined reference to `dlm_posix_get'
file.c:(.text+0xc7ad0): undefined reference to `dlm_posix_unlock'
file.c:(.text+0xc7ad9): undefined reference to `dlm_posix_lock'
fs/built-in.o: In function `gdlm_unmount':
lock_dlm.c:(.text+0xd6e5b): undefined reference to `dlm_release_lockspace'
fs/built-in.o: In function `sync_unlock':
lock_dlm.c:(.text+0xd6e9e): undefined reference to `dlm_unlock'
fs/built-in.o: In function `sync_lock':
lock_dlm.c:(.text+0xd6fb6): undefined reference to `dlm_lock'
fs/built-in.o: In function `gdlm_put_lock':
lock_dlm.c:(.text+0xd7238): undefined reference to `dlm_unlock'
fs/built-in.o: In function `gdlm_mount':
lock_dlm.c:(.text+0xd753e): undefined reference to `dlm_new_lockspace'
lock_dlm.c:(.text+0xd79d3): undefined reference to `dlm_release_lockspace'
fs/built-in.o: In function `gdlm_lock':
lock_dlm.c:(.text+0xd8179): undefined reference to `dlm_lock'
fs/built-in.o: In function `gdlm_cancel':
lock_dlm.c:(.text+0xd6b22): undefined reference to `dlm_unlock'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>