driver core: Check if r->name is valid in platform_get_resource_byname()

Safety check for the validity of the resource name before calling strcmp().
If the resource name is NULL do not compare it, just skip it.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>