ixp4xx: fix spelling mistake in Kconfig "Devce" -> "Device"

There is spelling mistake in the prompt text in the Kconfig. Fix it.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

arch/arm/mach-ixp4xx/Kconfig

@@ -7,7 +7,7 @@ comment "IXP4xx Platforms"
 
 config MACH_IXP4XX_OF
 	bool
-	prompt "Devce Tree IXP4xx boards"
+	prompt "Device Tree IXP4xx boards"
 	default y
 	select ARM_APPENDED_DTB # Old Redboot bootloaders deployed
 	select I2C