driver core: platform: Declare early_platform_cleanup() prototype

Compiler is not happy:

CC drivers/base/platform.o
drivers/base/platform.c:1557:20: warning: no previous prototype for ‘early_platform_cleanup’ [-Wmissing-prototypes]
1557 | void __weak __init early_platform_cleanup(void) { }
| ^~~~~~~~~~~~~~~~~~~~~~

Declare early_platform_cleanup() prototype in the header to make everyone happy.

Fixes: eecd37e105f0 ("drivers: Fix boot problem on SuperH")
Cc: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210331150525.59223-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>