SUNRPC: Use correct argument type in memcpy()

Noticed by Tom Talpey <tmt@netapp.com>:

OBTW, there's a nit on that memcpy, too. The r_addr is an array, so

memcpy(&map->r_addr

is passing the address of the array as a char **. It's the same as
map->r_addr, but technically the wrong type.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>