MAINTAINERS: add ksysfs.c to the DRIVER CORE entry

kernel/ksysfs.c is part of the driver core infrastructure but is missing
rom the relevant MAINTAINERS entry. Add it.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Closes: https://lore.kernel.org/all/DHITFGL3J4IE.2WZU3K2CSYL7I@kernel.org/
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260403080917.7484-1-bartosz.golaszewski@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Bartosz Golaszewski

MAINTAINERS

@@ -7807,6 +7807,7 @@ F:	include/linux/fwnode.h
 F:	include/linux/kobj*
 F:	include/linux/property.h
 F:	include/linux/sysfs.h
+F:	kernel/ksysfs.c
 F:	lib/kobj*
 F:	rust/kernel/debugfs.rs
 F:	rust/kernel/debugfs/