fastboot: Fallback to "raw" partition type if fastboot hal isn't present

Fastboot format fails to wipe any partition that doesn't at least return
"raw" partition type. Also both android.hardware.fastboot@1.0-impl.pixel
and android.hardware.fastboot@1.1-impl-mock return FileSystemType::RAW
so I assume this is fine.

Change-Id: I5707bddb1ba32edb6359858853d7b1afbf138b9f
diff --git a/fastboot/device/variables.cpp b/fastboot/device/variables.cpp
index 76e9889..0cf4699 100644
--- a/fastboot/device/variables.cpp
+++ b/fastboot/device/variables.cpp
@@ -332,8 +332,8 @@
 
     auto fastboot_hal = device->fastboot_hal();
     if (!fastboot_hal) {
-        *message = "Fastboot HAL not found";
-        return false;
+        *message = "raw";
+        return true;
     }
 
     FileSystemType type;