cros_firmware.py flashrom invocation fix

Added "-p host" to flashrom command line arguments so the programmer is properly detected on Grunt boards.

BUG=887032
TEST=None

Change-Id: I42d63f5b37d55a0dca9ec29ac4b052e23e225307
Reviewed-on: https://chromium-review.googlesource.com/1258533
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Chris McDonald <cjmcdonald@chromium.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
diff --git a/server/hosts/cros_firmware.py b/server/hosts/cros_firmware.py
index 232fa65..8971b69 100644
--- a/server/hosts/cros_firmware.py
+++ b/server/hosts/cros_firmware.py
@@ -154,7 +154,7 @@
             cmd = ('mkdir /tmp/verify_firmware; '
                    'cd /tmp/verify_firmware; '
                    'for section in VBLOCK_A VBLOCK_B FW_MAIN_A FW_MAIN_B; '
-                   'do flashrom -r -i $section:$section; '
+                   'do flashrom -p host -r -i $section:$section; '
                    'done')
             host.run(cmd)