intelmetool: handle failures to mmap MEI memory

Fixes crashes when there is an error mapping memory.

    Error mapping physical memory 0x0000004275159040 [0x4000] ERRNO=1
    Segmentation fault (core dumped)

Change-Id: I5becc0c2870dd97297c4e8d1b101b95b31792ca7
Signed-off-by: Paul Wise <pabs3@bonedaddy.net>
Reviewed-on: https://review.coreboot.org/19562
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/intelmetool/me.c

@@ -581,6 +581,10 @@ uint32_t intel_mei_setup(struct pci_dev *dev)
 	mei_base_address = dev->base_addr[0] & ~0xf;
 	pagerounded = mei_base_address & ~0xfff;
 	mei_mmap = map_physical(pagerounded, 0x2000) + mei_base_address - pagerounded;
+	if (mei_mmap == NULL) {
+		printf("Could not map ME setup memory\n");
+		return 1;
+	}
 
 	/* Ensure Memory and Bus Master bits are set */
 	reg32 = pci_read_long(dev, PCI_COMMAND);