crypto: picoxcell - Fix the name of the module in the description of CRYPTO_DEV_PICOXCELL

The help section says that the module will be called 'pipcoxcell_crypto'.
This is likely a typo.
Use 'picoxcell_crypto' instead

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>