hypfs_kill_super(): deal with failed allocations

[ Upstream commit a24cd490 ]

hypfs_fill_super() might fail to allocate sbi; hypfs_kill_super()
should not oops on that.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>