of/device: Nullify match table in of_match_device() for CONFIG_OF=n

If the of_device_id table inside a device driver is protected by #ifdef
CONFIG_OF, the driver still has to provide a dummy declaration of the
table, or wrap it inside of_match_ptr(), when calling of_match_device()
in the CONFIG_OF=n case, else the driver fails to compile with e.g.

drivers/spi/spi-rspi.c: In function 'rspi_probe':
drivers/spi/spi-rspi.c:1203:26: error: 'rspi_of_match' undeclared (first use in this function)
drivers/spi/spi-rspi.c:1203:26: note: each undeclared identifier is reported only once for each function it appears in

Make of_match_device() nullify the table pointer if CONFIG_OF=n to fix
this.

Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Signed-off-by: Rob Herring <robh@kernel.org>