fuse: Uninitialized variable in fuse_epoch_work()

fuse: Uninitialized variable in fuse_epoch_work()

The fuse_ilookup() function only sets *fm on the success path so this
"if (fm) {" NULL check doesn't work.  The "fm" pointer is either
uninitialized or valid.  Check the "inode" pointer instead.

Also, while it's not necessary, it is cleaner to move the iput(inode)
under the NULL check as well.

Fixes: 64becd224ff9 ("fuse: new work queue to invalidate dentries from old epochs")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Luis Henriques <luis@igalia.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>