[pci] Cache ECAM mapping errors

When an error occurs during ECAM configuration space mapping, preserve
the error within the existing cached mapping (instead of invalidating
the cached mapping) in order to avoid flooding the debug log with
repeated identical mapping errors.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/ecam.h

@@ -50,6 +50,8 @@ struct ecam_mapping {
 	struct pci_range range;
 	/** MMIO base address */
 	void *regs;
+	/** Mapping result */
+	int rc;
 };
 
 extern struct pci_api ecam_api;