regulator: mt6315: Fix checking return value of devm_regmap_init_spmi_ext

devm_regmap_init_spmi_ext() returns ERR_PTR() on error.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20210615132934.3453965-1-axel.lin@ingics.com


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