MAINTAINERS: use include/linux/reset for reset controller related headers

The include/linux/reset directory currently contains one header with
helper functions for Broadcom BCM63xx PMB, which can control reset
lines to on-chip peripherals. Even though that driver doesn't use the
reset controller framework, the the directory can be shared with other
reset controller drivers that do.

Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>