commit 6b7f4e25 upstream.

All regulator_get() variants return either a pointer to a regulator or an
ERR_PTR() so testing for NULL makes no sense and may lead to bugs if we
use NULL as a valid regulator. Fix this by using IS_ERR() as expected.
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>