Don't cast the pointer past to memset

Don't cast the pointer past to memset

memset() takes a void * as it's first argument. Don't explicitly cast
what we're passing in to (char *), as this may mask other errors.

Reviewed-on: http://gerrit.openafs.org/701
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>