cxl/mem: Drop mem_enabled check from wait_for_media()

Media ready is asserted by the device independent of whether mem_enabled
was ever set. Drop this check to allow for dropping wait_for_media() in
favor of ->wait_media_ready().

Fixes: 8dd2bc0f ("cxl/mem: Add the cxl_mem driver")
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165291685501.1426646.10372821863672431074.stgit@dwillia2-xfh


Signed-off-by: Dan Williams <dan.j.williams@intel.com>