Fix up a few callers of GetTypeAndDevice.

Change-Id: I8f2d8d28b60715f917e9aceb8f851ad652034aa7
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 63e438a..f76f812 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -1252,14 +1252,11 @@
   _, _, patch = d.ComputePatch()
   output_sink("recovery-from-boot.p", patch)
 
-  td_pair = GetTypeAndDevice("/boot", info_dict)
-  if not td_pair:
+  try:
+    boot_type, boot_device = GetTypeAndDevice("/boot", info_dict)
+    recovery_type, recovery_device = GetTypeAndDevice("/recovery", info_dict)
+  except KeyError:
     return
-  boot_type, boot_device = td_pair
-  td_pair = GetTypeAndDevice("/recovery", info_dict)
-  if not td_pair:
-    return
-  recovery_type, recovery_device = td_pair
 
   sh = """#!/system/bin/sh
 if ! applypatch -c %(recovery_type)s:%(recovery_device)s:%(recovery_size)d:%(recovery_sha1)s; then