serial: s3c: Update path of Samsung S3C machine file

Correct the path to Samsung S3C24xx machine file, mentioned in
documentation.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200911143343.498-2-krzk@kernel.org

include/linux/serial_s3c.h

@@ -254,7 +254,7 @@
  * serial port
  *
  * the pointer is setup by the machine specific initialisation from the
- * arch/arm/mach-s3c2410/ directory.
+ * arch/arm/mach-s3c/ directory.
 */
 
 struct s3c2410_uartcfg {