regulator: core: Fix deadlock in create_regulator()

regulator: core: Fix deadlock in create_regulator()

Currently, we are unnecessarily holding a regulator_ww_class_mutex lock
when creating debugfs entries for a newly created regulator. This was
brought up as a concern in the discussion in commit cba6cfdc7c3f
("regulator: core: Avoid lockdep reports when resolving supplies").

This causes the following lockdep splat after executing
`ls /sys/kernel/debug` on my platform:

  ======================================================
  WARNING: possible circular locking dependency detected
  5.15.167-axis9-devel #1 Tainted: G           O
  ------------------------------------------------------
  ls/2146 is trying to acquire lock:
  ffffff803a562918 (&mm->mmap_lock){++++}-{3:3}, at: __might_fault+0x40/0x88

  but task is already holding lock:
  ffffff80014497f8 (&sb->s_type->i_mutex_key#3){++++}-{3:3}, at: iterate_dir+0x50/0x1f4

  which lock already depends on the new lock.

  [...]

  Chain exists of:
    &mm->mmap_lock --> regulator_ww_class_mutex --> &sb->s_type->i_mutex_key#3

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(&sb->s_type->i_mutex_key#3);
                                 lock(regulator_ww_class_mutex);
                                 lock(&sb->s_type->i_mutex_key#3);
    lock(&mm->mmap_lock);

   *** DEADLOCK ***

This lock dependency still exists on the latest kernel and using a newer
non-tainted kernel would still cause this problem.

Fix by moving sysfs symlinking and creation of debugfs entries to after
the release of the regulator lock.

Fixes: cba6cfdc7c3f ("regulator: core: Avoid lockdep reports when resolving supplies")
Fixes: eaa7995c529b ("regulator: core: avoid regulator_resolve_supply() race condition")
Signed-off-by: Ludvig Pärsson <ludvig.parsson@axis.com>
Link: https://patch.msgid.link/20250305-regulator_lockdep_fix-v1-1-ab938b12e790@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>