pinctrl: imx51: fix .conf_reg of MX51_PAD_SD2_CMD__CSPI_MOSI

The .conf_reg of MX51_PAD_SD2_CMD__CSPI_MOSI should be 0x7bc rather
than NO_PAD.  This error will cause SD2 probe failure.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>