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/nicintel_spi.c b/nicintel_spi.c
index b1bce6a..11b26c7 100644
--- a/nicintel_spi.c
+++ b/nicintel_spi.c
@@ -173,6 +173,9 @@
 		return 1;
 
 	io_base_addr = pcidev_readbar(dev, PCI_BASE_ADDRESS_0);
+	if (!io_base_addr)
+		return 1;
+
 	nicintel_spibar = rphysmap("Intel Gigabit NIC w/ SPI flash", io_base_addr, MEMMAP_SIZE);
 	/* Automatic restore of EECD on shutdown is not possible because EECD
 	 * does not only contain FLASH_WRITES_DISABLED|FLASH_WRITES_ENABLED,