Fix a warning while compiling with GCC 5.4.0 (OSELAS.Toolchain 2016.02):

    drivers/pinctrl/imx-iomux-v3.c: In function 'imx_iomux_v3_set_state':
    drivers/pinctrl/imx-iomux-v3.c:153:13: warning: 'share_conf_val' may be used uninitialized in this function [-Wmaybe-uninitialized]
        conf_val &= ~IMX_PAD_SION;

we have the pattern:

	if (share_conf)
		share_conf_val = ...;
	...

	if (share_conf)
		use(share_conf_val);

GCC 5.4.0 doesn't recognize this so explicitly initialize
share_conf_val.

Signed-off-by: Roland Hieber <rohieb@rohieb.name>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>