Fix build from -Werror=maybe-uninitialized.

This won't actually ever be uninitialized because the code will take a
failure path if the code that initializes it fails. The goto seems to
thwart this check though.

Not sure why this is only firing on userdebug builds yet. I'll look in
to it tomorrow.

Change-Id: Ie9d837d6baea255d2a4d169355b53dfd775eacce

adb/set_verity_enable_state_service.cpp

@@ -90,7 +90,7 @@ static int set_verity_enabled_state(int fd, const char *block_device,
     uint32_t magic_number;
     const uint32_t new_magic = enable ? VERITY_METADATA_MAGIC_NUMBER
                                       : VERITY_METADATA_MAGIC_DISABLE;
-    uint64_t device_length;
+    uint64_t device_length = 0;
     int device = -1;
     int retval = -1;