crytpfs: fix clobbering of crypto info on keymaster failure

crytpfs: fix clobbering of crypto info on keymaster failure

Changing the device lock (even from swipe to none) will cause the
master key to be re-encrypted.
If at that point keymaster fails (e.g. due to an incompatible keymaster update)
cryptfs will write back the now-incomplete crypto metadata.
Upon next reboot, userdata can't be decrypted.

Now we don't bother writing on keymaster failure.

Bug: 19301883
Change-Id: I2b9a1278f8b4d333ac8d567e17e2263005e99409