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

drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c: In function 'rmnet_map_do_flow_control':
drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c:23:36: warning:
 variable 'cmd' set but not used [-Wunused-but-set-variable]
  struct rmnet_map_control_command *cmd;

'cmd' not used anymore now, should also be removed.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>