arm: Typo s/PCI_IXP4XX_LEGACY/IXP4XX_PCI_LEGACY/

Kconfig symbol PCI_IXP4XX_LEGACY does not exist, but IXP4XX_PCI_LEGACY
does.

Fixes: d5d9f7ac ("ARM/ixp4xx: Make NEED_MACH_IO_H optional")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/82ce37c617293521f095a945a255456b9512769c.1626255077.git.geert+renesas@glider.be'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/Kconfig

@@ -395,7 +395,7 @@ config ARCH_IXP4XX
 	select IXP4XX_IRQ
 	select IXP4XX_TIMER
 	# With the new PCI driver this is not needed
-	select NEED_MACH_IO_H if PCI_IXP4XX_LEGACY
+	select NEED_MACH_IO_H if IXP4XX_PCI_LEGACY
 	select USB_EHCI_BIG_ENDIAN_DESC
 	select USB_EHCI_BIG_ENDIAN_MMIO
 	help