cxl/pci: Check memdev driver binding status in cxl_reset_done()

cxl/pci: Check memdev driver binding status in cxl_reset_done()

cxl_reset_done() accesses the endpoint of the corresponding CXL memdev
without endpoint validity checking. By default, cxlmd->endpoint is
initialized to -ENXIO, if cxl_reset_done() is triggered after the
corresponding CXL memdev probing failed, this results in access to an
invalid endpoint.

CXL subsystem can always check CXL memdev driver binding status to
confirm its endpoint validity. So adding the CXL memdev driver checking
inside cxl_reset_done() to avoid accessing an invalid endpoint.

Fixes: 934edcd436dc ("cxl: Add post-reset warning if reset results in loss of previously committed HDM decoders")
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Li Ming <ming.li@zohomail.com>
Link: https://patch.msgid.link/20260314-fix_access_endpoint_without_drv_check-v2-4-4c09edf2e1db@zohomail.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>