mainboard/purism/librem_skl: Fix line length > 80 characters

Make lint-stable was giving an error on this.

Change-Id: I06d11d86151f683b82b6df537e3de8c52d33e8b4
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/22811
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Youness Alaoui <snifikino@gmail.com>

src/mainboard/purism/librem_skl/mainboard.c

@@ -43,7 +43,8 @@ const char *smbios_mainboard_serial_number(void)
 		}
 	}
 
-	strncpy(serial_number, CONFIG_MAINBOARD_SERIAL_NUMBER, MAX_SERIAL_LENGTH);
+	strncpy(serial_number, CONFIG_MAINBOARD_SERIAL_NUMBER,
+			MAX_SERIAL_LENGTH);
 
 	return serial_number;
 }