PCI: endpoint: Return error if EPC is started/stopped multiple times

When the EPC is started or stopped multiple times from configfs, just
return -EALREADY. There is no need to call the EPC start/stop functions
in those cases.

Link: https://lore.kernel.org/r/20230602114756.36586-4-manivannan.sadhasivam@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kishon Vijay Abraham I <kishon@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

Author: Mani-Sadhasivam

drivers/pci/endpoint/pci-ep-cfs.c

@@ -179,6 +179,9 @@ static ssize_t pci_epc_start_store(struct config_item *item, const char *page,
 	if (kstrtobool(page, &start) < 0)
 		return -EINVAL;
 
+	if (start == epc_group->start)
+		return -EALREADY;
+
 	if (!start) {
 		pci_epc_stop(epc);
 		epc_group->start = 0;