spi: spi-mtk-nor: make some internal variables static

Variables mtk_nor_caps_mt8173, mtk_nor_caps_mt8186 and
mtk_nor_caps_mt8192 are not declared.
Make them static.

Fixes: 5b177234 ("spi: spi-mtk-nor: improve device table for adding more capabilities")
Signed-off-by: Guochun Mao <guochun.mao@mediatek.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20220126091159.27513-1-guochun.mao@mediatek.com


Signed-off-by: Mark Brown <broonie@kernel.org>