net/smc: eliminate cursor read and write calls

The functions to read and write cursors are exclusively used to copy
cursors. Therefore switch to a respective function instead.

Signed-off-by: Stefan Raspl <raspl@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>