crypto: inside-secure - improve clock initialization

The clock is optional, but if it is present we should managed it. If
there is an error while trying getting it, we should exit and report this
error.

So instead of returning an error only in the -EPROBE case, turn it in an
other way and ignore the clock only if it is not present (-ENOENT case).

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>