Add additional error handling to pcidev_readbar() callers

This is mostly a leftover of Niklas' "remove exit call from pcidev_init" patch.
While not explicitly necessary detecting errors early is usually a good idea.

Corresponding to flashrom svn r1718.

Signed-off-by: Niklas Söderlund <niso@kth.se>
Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
diff --git a/atahpt.c b/atahpt.c
index f8be8c4..242e14a 100644
--- a/atahpt.c
+++ b/atahpt.c
@@ -69,6 +69,8 @@
 		return 1;
 
 	io_base_addr = pcidev_readbar(dev, PCI_BASE_ADDRESS_4);
+	if (!io_base_addr)
+		return 1;
 
 	/* Enable flash access. */
 	reg32 = pci_read_long(dev, REG_FLASH_ACCESS);