MAINTAINERS: Add git tree for NVMEM FRAMEWORK

There is no git tree for NVMEM FRAMEWORK in MAINTAINERS, it is not
convinent to rebase, add it.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200722100705.7772-3-srinivas.kandagatla@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>