regulator: da9121: Remove uninitialised string variable

Erroneously left in when switched to using of_parse_cb()

Signed-off-by: Adam Ward <Adam.Ward.opensource@diasemi.com>
Link: https://lore.kernel.org/r/c7a9e947a9582fe0150d860b5eab7e093cd832bb.1607361013.git.Adam.Ward.opensource@diasemi.com


Signed-off-by: Mark Brown <broonie@kernel.org>