PCI: endpoint: Return -EINVAL when interrupts num is smaller than 1

In pci_epc_set_msi() we should return immediately if there are no
interrupts to configure; update the code to return early.

Link: https://lore.kernel.org/r/CH2PR19MB402491B9E503694DBCAC6005A07C9@CH2PR19MB4024.namprd19.prod.outlook.com


Signed-off-by: Li Chen <lchen@ambarella.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>