regulator: core: Streamline debugfs operations

If CONFIG_DEBUG_FS is not set:

    regulator: Failed to create debugfs directory
    ...
    regulator-dummy: Failed to create debugfs directory

As per the comments for debugfs_create_dir(), errors returned by this
function should be expected, and ignored:

 * If debugfs is not enabled in the kernel, the value -%ENODEV will be
 * returned.
 *
 * NOTE: it's expected that most callers should _ignore_ the errors returned
 * by this function. Other debugfs functions handle the fact that the "dentry"
 * passed to them could be an error and they don't crash in that case.
 * Drivers should generally work fine even if debugfs fails to init anyway.

Adhere to the debugfs spirit, and streamline all operations by:
  1. Demoting the importance of the printed error messages to debug
     level, like is already done in create_regulator(),
  2. Further ignoring any returned errors, as by design, all debugfs
     functions are no-ops when passed an error pointer.

Fixes: 2bf1c45b

 ("regulator: Fix error checking for debugfs_create_dir")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/2f8bb6e113359ddfab7b59e4d4274bd4c06d6d0a.1685013051.git.geert+renesas@glider.be
Signed-off-by: Mark Brown <broonie@kernel.org>