crypto: api - Only abort operations on fatal signal

commit 3fc89adb upstream.

Currently a number of Crypto API operations may fail when a signal
occurs.  This causes nasty problems as the caller of those operations
are often not in a good position to restart the operation.

In fact there is currently no need for those operations to be
interrupted by user signals at all.  All we need is for them to
be killable.

This patch replaces the relevant calls of signal_pending with
fatal_signal_pending, and wait_for_completion_interruptible with
wait_for_completion_killable, respectively.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[bwh: Backported to 3.2: drop change to crypto_user_skcipher_alg(), which
 we don't have]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>