mtd: physmap_of_gemini: remove defined but not used symbol 'syscon_match'

It's not used by anyone now, remove it. Fix the following gcc warning:

drivers/mtd/maps/physmap-gemini.c:49:34: warning: ‘syscon_match’ defined
but not used [-Wunused-const-variable=]
 static const struct of_device_id syscon_match[] = {
                                  ^~~~~~~~~~~~

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Richard Weinberger <richard@nod.at>