PCI: endpoint: Introduce pci_epc_function_is_valid()

PCI: endpoint: Introduce pci_epc_function_is_valid()

Introduce the epc core helper function pci_epc_function_is_valid() to
verify that an epc pointer, a physical function number and a virtual
function number are all valid. This avoids repeating the code pattern:

if (IS_ERR_OR_NULL(epc) || func_no >= epc->max_functions)
	return err;

if (vfunc_no > 0 && (!epc->max_vfs || vfunc_no > epc->max_vfs[func_no]))
	return err;

in many functions of the endpoint controller core code.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Link: https://lore.kernel.org/r/20241012113246.95634-2-dlemoal@kernel.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>