MAINTAINERS: ARM Versatile Express platform, add missing pattern

VE's reset driver lives at the third level of the directories:

	drivers/power/reset/vexpress-poweroff.c

and wasn't matched by the */*/vexpress* pattern.

Added additional pattern for all files at this level. This should be
enough for a while...

Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>