net: pktgen: fix code style (ERROR: "foo * bar" should be "foo *bar")

Fix checkpatch code style errors:

  ERROR: "foo * bar" should be "foo *bar"
  #977: FILE: net/core/pktgen.c:977:
  +                              const char __user * user_buffer, size_t count,

  ERROR: "foo * bar" should be "foo *bar"
  #978: FILE: net/core/pktgen.c:978:
  +                              loff_t * offset)

  ERROR: "foo * bar" should be "foo *bar"
  #1912: FILE: net/core/pktgen.c:1912:
  +                                  const char __user * user_buffer,

  ERROR: "foo * bar" should be "foo *bar"
  #1913: FILE: net/core/pktgen.c:1913:
  +                                  size_t count, loff_t * offset)

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>