nvmem: mtk-efuse: Remove EFUSE register write support

nvmem: mtk-efuse: Remove EFUSE register write support

This patch is to remove function "mtk_reg_write" since
Mediatek EFUSE hardware only supports read functionality
for NVMEM consumers.

Fixes: ba360fd040e3 ("nvmem: mtk-efuse: remove nvmem regmap dependency")
Acked-by: Andrew-CT Chen <andrew-ct.chen@mediatek.com>
Signed-off-by: Chih-En Hsu <chih-en.hsu@mediatek.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200917134437.16637-2-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>