moduleparam: Resolve missing-field-initializer warning

Resolve a missing-field-initializer warning, that is produced
by every reference to module_param_call, by using designated
initialization for the first field. That is enough to silence
the complaint.

The message is only seen when doing a W=2 build. I happened to be using gcc
4.8.3, but I think most versions would produce the warning when it is
enabled. It can either be silenced by using even a single designated
initializer as I did here, or providing values for all of the fields. Because
of the number of references to the macro, this change silences many warnings
in W=2 builds.

One instance of the full warning message looks like this:

/home/share/git/nn-mdr/include/linux/moduleparam.h:198:16: warning: missing
initializer for field ‘free’ of ‘struct kernel_param_ops’
[-Wmissing-field-initializers]
  static struct kernel_param_ops __param_ops_##name =  \
		  ^
/home/share/git/nn-mdr/fs/fuse/inode.c:35:1: note: in expansion of macro
‘module_param_call’
 module_param_call(max_user_bgreq, set_global_limit, param_get_uint,
 ^
/home/share/git/nn-mdr/include/linux/moduleparam.h:56:9: note: ‘free’
declared here
  void (*free)(void *arg);

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>