btrfs: add missing commit ids for a few tests using _fixed_by_kernel_commit

btrfs: add missing commit ids for a few tests using _fixed_by_kernel_commit

The tests btrfs/288, btrfs/289 and btrfs/300 are using the "xxxx..." stub
for commit ids, as when they were submitted/merged the corresponding
btrfs patches were not yet in Linus' tree. So replace the stubs with the
commit ids.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>