cxl: Fix NULL dereference in cxl_context_init() on PowerVM guests

Commit f67a6722d6 ("cxl: Workaround PE=0 hardware limitation in
Mellanox CX4") added a "min_pe" field to struct cxl_service_layer_ops,
to allow us to work around a Mellanox CX-4 hardware limitation.

When allocating the PE number in cxl_context_init(), we read from
ctx->afu->adapter->native->sl_ops->min_pe to get the minimum PE number.
Unsurprisingly, in a PowerVM guest ctx->afu->adapter->native is NULL,
and guests don't have a cxl_service_layer_ops struct anywhere.

Move min_pe from struct cxl_service_layer_ops to struct cxl so it's
accessible in both native and PowerVM environments. For the Mellanox
CX-4, set the min_pe value in set_sl_ops().

Fixes: f67a6722d6 ("cxl: Workaround PE=0 hardware limitation in Mellanox CX4")
Reported-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Reviewed-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/context.c

@@ -90,8 +90,7 @@ int cxl_context_init(struct cxl_context *ctx, struct cxl_afu *afu, bool master,
 	 */
 	mutex_lock(&afu->contexts_lock);
 	idr_preload(GFP_KERNEL);
-	i = idr_alloc(&ctx->afu->contexts_idr, ctx,
-		      ctx->afu->adapter->native->sl_ops->min_pe,
+	i = idr_alloc(&ctx->afu->contexts_idr, ctx, ctx->afu->adapter->min_pe,
 		      ctx->afu->num_procs, GFP_NOWAIT);
 	idr_preload_end();
 	mutex_unlock(&afu->contexts_lock);