sfc: refactor code in efx_ef10_set_mac_address()

Re-organize the structure of error handling to avoid having
to duplicate the netif_err() around the ifdefs.

The only change to the behaviour of the error-handling is that
the PF's data structure to record VF details should only be
updated if the original command succeeded.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>