kernel: fix regression in building kmod-serial-8250 on linux 3.8 (#18821)

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 44154

package/kernel/linux/modules/other.mk

@@ -698,7 +698,7 @@ define KernelPackage/serial-8250
 	CONFIG_SERIAL_8250_SHARE_IRQ=y \
 	CONFIG_SERIAL_8250_DETECT_IRQ=n \
 	CONFIG_SERIAL_8250_RSA=n
-  FILES:=$(LINUX_DIR)/drivers/tty/serial/8250/8250.ko
+  FILES:=$(LINUX_DIR)/drivers/tty/serial/8250/8250$(if $(CONFIG_LINUX_3_8),_core).ko
 endef
 
 define KernelPackage/serial-8250/description