scsi: isci: Add a missing call to pci_unmap_biosrom

Most error branches following the call to pci_map_biosrom contain a call
to pci_unmap_biosrom. This patch add these calls where they are missing.

This issue was found with Hector.

Signed-off-by: Quentin Lambert <lambert.quentin@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>