mtd: core: call _get_device() with the master MTD

In the Linux kernel, the following vulnerability has been resolved: mtd: core: call _get_device() with the master MTD __get_mtd_device() calls the master's _get_device() callback with mtd, which may be a partition. __put_mtd_device() passes the master. This breaks gluebi partitions because gluebi_get_device() uses container_of() and therefore requires the master MTD. Pass the master to _get_device(), matching _put_device().

Where it's fixed