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

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
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20251109201729.3220460-1-andriy.shevchenko@linux.intel.com
Reviewed-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>