rxfs_storePadd: return 0 on success

rxfs_storePadd: return 0 on success

On success, storePadd should return 0, not the number of bytes
written by the last rx_Write call.  In some cases this return
value would leak all the way out to the close() system call,
causing it to fail.

Reviewed-on: http://gerrit.openafs.org/573
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>