btrfs-progs: build btrfs.static needs libbtrfsutil to build

btrfs-progs: build btrfs.static needs libbtrfsutil to build

Add libbtrfsutil objects to btrfs.static link command. This fixes static
build failure:

utils.static.o: In function `parse_qgroupid':
utils.c:(.text.parse_qgroupid+0xb0): undefined reference to `btrfs_util_is_subvolume'
props.static.o: In function `prop_read_only':
props.c:(.text.prop_read_only+0x70): undefined reference to `btrfs_util_set_subvolume_read_only'
...
Makefile:457: recipe for target 'btrfs.static' failed
make[1]: *** [btrfs.static] Error 1

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: David Sterba <dsterba@suse.com>