regulator: dbx500: use seq_puts() instead of seq_printf()

For a constant format without additional arguments, use seq_puts()
instead of seq_printf(). Also, it fixes the following checkpatch
warning.

  WARNING: Prefer seq_puts to seq_printf

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>