pinctrl: freescale: add ZERO_OFFSET_VALID flag for vf610 pinctrl

To support i.MX7D Low Power State Retention IOMUXC, commit e7b37a52
("pinctrl: freescale: imx: allow mux_reg offset zero") changes the way
of zero mux_reg offset support with a new flag ZERO_OFFSET_VALID.  But,
unfortunately, it forgot to add this flag for vf610 pinctrl which has
zero mux_reg offset be valid as well, and hence breaks the vf610
support.

Fix the regression by adding flag ZERO_OFFSET_VALID for vf610 pinctrl
driver.

Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Fixes: e7b37a52 ("pinctrl: freescale: imx: allow mux_reg offset zero")
Reported-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>