staging: ccree: remove unneeded cast

Remove unneeded cast of the return value of dev_get_drvdata()
to struct ssi_drvdata * for better readability.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>