fs/namespace: fix reference leak in grab_requested_mnt_ns

fs/namespace: fix reference leak in grab_requested_mnt_ns

[ Upstream commit 7b6dcd9bfd869eee7693e45b1817dac8c56e5f86 ]

lookup_mnt_ns() already takes a reference on mnt_ns.
grab_requested_mnt_ns() doesn't need to take an extra reference.

Fixes: 78f0e33cd6c93 ("fs/namespace: correctly handle errors returned by grab_requested_mnt_ns")
Signed-off-by: Andrei Vagin <avagin@google.com>
Link: https://patch.msgid.link/20251122071953.3053755-1-avagin@google.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>