staging/line6: Fix kzalloc coding style issue

Pass the actual variable to sizeof instead of a type definition.

Signed-off-by: L. Alberto Giménez <agimenez@sysvalve.es>
Acked-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>