arm: fix run script testdev probing

Using -kernel doesn't force qemu to exit immediately,
and thus we "hang" when trying to run arm/run. Using
-initrd works though.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arm/run b/arm/run
index a714350..4c5e525 100755
--- a/arm/run
+++ b/arm/run
@@ -26,7 +26,7 @@
 	exit 2
 fi
 
-if $qemu $M -chardev testdev,id=id -kernel . 2>&1 \
+if $qemu $M -chardev testdev,id=id -initrd . 2>&1 \
 		| grep backend > /dev/null; then
 	echo "$qpath doesn't support chr-testdev. Exiting."
 	exit 2