regulator: da9063: Fix PTR_ERR/ERR_PTR mismatch

If CONFIG_OF=n:

drivers/regulator/da9063-regulator.c: In function ‘da9063_parse_regulators_dt’:
drivers/regulator/da9063-regulator.c:712: warning: passing argument 1 of ‘PTR_ERR’ makes pointer from integer without a cast
drivers/regulator/da9063-regulator.c:712: warning: return makes pointer from integer without a cast

Use ERR_PTR() to encode an error code in a pointer.
PTR_ERR() is meant to decode an error code from a pointer.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Mark Brown <broonie@linaro.org>