staging: mfd: hi6421-spmi-pmic: fix some coding style issues

Checkpatch complains about some minor issues inside this
driver that were not addressed by the previous patch.

Address them.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/84b53d20632c84cc60b8dadfe937f3c54b355cef.1597647359.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>