MAINTAINERS: Adjust the file entry for the qnap-mcu header

MAINTAINERS: Adjust the file entry for the qnap-mcu header

Commit 998f70d1806b ("mfd: Add base driver for qnap-mcu devices") adds a
file entry in MAINTAINERS referring to the file include/linux/qnap-mcu.h,
whereas the file added in the commit is placed in include/linux/mfd/.

Adjust the file entry to the actual location of this header file.

Fixes: 998f70d1806b ("mfd: Add base driver for qnap-mcu devices")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Link: https://lore.kernel.org/r/20250110120736.58831-1-lukas.bulwahn@redhat.com
Signed-off-by: Lee Jones <lee@kernel.org>