misc: ocxl: fix possible double free in ocxl_file_register_afu

info_release() will be called in device_unregister() when info->dev's
reference count is 0. So there is no need to call ocxl_afu_put() and
kfree() again.

Fix this by adding free_minor() and return to err_unregister error path.

Fixes: 75ca758a ("ocxl: Create a clear delineation between ocxl backend & frontend")
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Acked-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220418085758.38145-1-hbh25y@gmail.com