pid: Fix error return value in some cases

pid: Fix error return value in some cases

Recent changes to alloc_pid() allow the pid number to be specified on
the command line.  If set_tid_size is set, then the code scanning the
levels will hard-set retval to -EPERM, overriding it's previous -ENOMEM
value.

After the code scanning the levels, there are error returns that do not
set retval, assuming it is still set to -ENOMEM.

So set retval back to -ENOMEM after scanning the levels.

Fixes: 49cb2fc42ce4 ("fork: extend clone3() to support setting a PID")
Signed-off-by: Corey Minyard <[email protected]>
Acked-by: Christian Brauner <[email protected]>
Cc: Andrei Vagin <[email protected]>
Cc: Dmitry Safonov <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Adrian Reber <[email protected]>
Cc: <[email protected]> # 5.5
Link: https://lore.kernel.org/r/[email protected]
[[email protected]: fixup commit message]
Signed-off-by: Christian Brauner <[email protected]>