staging/easycap: Fix thinko in "bars" module option description

Both bars=0 and bars=1 were described as meaning to display bars on
signal lost. Actually bars=1 means "display bars", but bars=0 means
display raw source as is (usually black screen).

Instead of changing bars=0 to "_no_ testcard bars ..." as suggested by
Dan Carpenter reword the whole bars description for clarity.

Cc: Mike Thomas <rmthomas@sciolus.org>
Cc: Dan Carpenter <error27@gmail.com>
Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>