Fixes below warning by dynamically allocating memory

All warnings:

   drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c: In function
   'cctrl_tbl_show':
   >> drivers/net/ethernet/chelsio/cxgb4/cxgb4_debugfs.c:689:1: warning: the
   >> frame
   >> size of 1028 bytes is larger than 1024 bytes [-Wframe-larger-than=]
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>