Driver core: Make platform_device_add_data accept a const pointer

platform_device_add_data() makes a copy of the data that is given to it,
and thus the parameter can be const.  This removes a warning when data
from get_property() on powerpc is handed to platform_device_add_data(),
as get_property() returns a const pointer.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>