MAINTAINERS: rectify MMP SUPPORT after moving cputype.h

Commit 32adcaa0 ("ARM: mmp: move cputype.h to include/linux/soc/")
added a file entry that does not point to the intended file location.

Since then, ./scripts/get_maintainer.pl --self-test complains:

  warning: no file matches F: linux/soc/mmp/

Rectify the MAINTAINERS entry now.

Fixes: 32adcaa0 ("ARM: mmp: move cputype.h to include/linux/soc/")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>