net: cdc_ncm: remove set but not used variable 'ctx'

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

drivers/net/usb/cdc_ncm.c: In function 'cdc_ncm_status':
drivers/net/usb/cdc_ncm.c:1603:22: warning:
 variable 'ctx' set but not used [-Wunused-but-set-variable]
  struct cdc_ncm_ctx *ctx;

It not used any more after
commit fa83dbee ("net: cdc_ncm: remove redundant "disconnected" flag")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>