fpga: altera-cvp: Use pci_find_vsec_capability() when probing FPGA device

Currently altera_cvp_probe() open-codes pci_find_vsec_capability().
Refactor the former to use the latter.

With that done:
- use the VSEC ID as per datasheet [1]
- update the error message accordingly

Link: https://www.intel.com/content/www/us/en/docs/programmable/683763/23-1/vendor-specific-header-register.html [1]
Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Xu Yilun <[e-mail]>
Signed-off-by: Xu Yilun <[e-mail]>

drivers/fpga/altera-cvp.c

···
 #define TIMEOUT_US	2000	/* CVP STATUS timeout for USERMODE polling */
 
 /* Vendor Specific Extended Capability Registers */
-#define VSE_PCIE_EXT_CAP_ID		0x0
-#define VSE_PCIE_EXT_CAP_ID_VAL		0x000b	/* 16bit */
-
 #define VSE_CVP_STATUS			0x1c	/* 32bit */
 #define VSE_CVP_STATUS_CFG_RDY		BIT(18)	/* CVP_CONFIG_READY */
 #define VSE_CVP_STATUS_CFG_ERR		BIT(19)	/* CVP_CONFIG_ERROR */
···
 {
 	struct altera_cvp_conf *conf;
 	struct fpga_manager *mgr;
-	int ret, offset;
-	u16 cmd, val;
+	u16 cmd, offset;
 	u32 regval;
-
-	/* Discover the Vendor Specific Offset for this device */
-	offset = pci_find_next_ext_capability(pdev, 0, PCI_EXT_CAP_ID_VNDR);
-	if (!offset) {
-		dev_err(&pdev->dev, "No Vendor Specific Offset.\n");
-		return -ENODEV;
-	}
+	int ret;
 
 	/*
 	 * First check if this is the expected FPGA device. PCI config
 	 * space access works without enabling the PCI device, memory
 	 * space access is enabled further down.
 	 */
-	pci_read_config_word(pdev, offset + VSE_PCIE_EXT_CAP_ID, &val);
-	if (val != VSE_PCIE_EXT_CAP_ID_VAL) {
-		dev_err(&pdev->dev, "Wrong EXT_CAP_ID value 0x%x\n", val);
+	offset = pci_find_vsec_capability(pdev, PCI_VENDOR_ID_ALTERA, 0x1172);
+	if (!offset) {
+		dev_err(&pdev->dev, "Wrong VSEC ID value\n");
 		return -ENODEV;
 	}