MAINTAINERS: claim maintainership of files with "uniphier" pattern

The pattern "N:    uniphier" can cover
  - drivers/serial/serial_uniphier.c
  - drivers/i2c/i2c-uniphier.c
  - drivers/i2c/i2c-uniphier-f.c
  - arch/arm/dts/uniphier-*

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>