Add an empty version of of_find_node_by_path().
This fixes following build error for asoc tree:
sound/soc/fsl/fsl_ssi.c: In function 'fsl_ssi_probe':
sound/soc/fsl/fsl_ssi.c:1471:2: error: implicit declaration of function 'of_find_node_by_path' [-Werror=implicit-function-declaration]
  sprop = of_get_property(of_find_node_by_path("/"), "compatible", NULL);
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NAlexander Shiyan <shc_work@mail.ru>
Signed-off-by: NRob Herring <robh@kernel.org>