[SERIAL] 8250: limit range of runtime ports

Prevent SERIAL_8250_RUNTIME_UARTS being larger than SERIAL_8250_NR_UARTS.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/serial/Kconfig

@@ -98,6 +98,7 @@ config SERIAL_8250_NR_UARTS
 config SERIAL_8250_RUNTIME_UARTS
 	int "Number of 8250/16550 serial ports to register at runtime"
 	depends on SERIAL_8250
+	range 0 SERIAL_8250_NR_UARTS
 	default "4"
 	help
 	  Set this to the maximum number of serial ports you want