ocelot: remove unused variable 'rc' in vcap_cmd()

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/mscc/ocelot_ace.c: In function ‘vcap_cmd’:
drivers/net/ethernet/mscc/ocelot_ace.c:108:6: warning: variable ‘rc’ set
but not used [-Wunused-but-set-variable]
  int rc;
      ^
It's never used since introduction in commit b5962294 ("net: mscc:
ocelot: Add support for tcam")

Signed-off-by: Mao Wenan <maowenan@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>