autofs: fix sbi->pipe file reference leak in autofs_kill_sb()

When autofs_fill_super() fails before clearing AUTOFS_SBI_CATATONIC (for
example, when find_get_pid() fails on an invalid pgrp mount option, or
when an fs_context is closed before mounting), deactivate_locked_super()
invokes autofs_kill_sb() -> autofs_catatonic_mode(sbi).

Because AUTOFS_SBI_CATATONIC is still set in sbi->flags,
autofs_catatonic_mode() returns early without calling fput(sbi->pipe),
permanently leaking the pipe struct file reference.

Explicitly release sbi->pipe in autofs_kill_sb() if it is still non-NULL
after autofs_catatonic_mode().

Fixes: ebc921ca9b92 ("autofs: copy autofs4 to autofs")
Signed-off-by: Hui Peng <benquike@gmail.com>
Link: https://patch.msgid.link/20260919204808.2812930-1-benquike@gmail.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>