ecryptfs: fix error handling

The error paths and the module exit code need work. sysfs
unregistration is not the right place to tear down the crypto
subsystem, and the code to undo subsystem initializations on various
error paths is unnecessarily duplicated. This patch addresses those
issues.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>