qibfs: fix _another_ leak

[ Upstream commit bdb43af4 ]

failure to allocate inode => leaked dentry...

this one had been there since the initial merge; to be fair,
if we are that far OOM, the odds of failing at that particular
allocation are low...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>