s can only be configured as a set of rising
and falling edges ('OR' mode) or as a set of high and low levels ('AND'
mode).  Preserve the old input channels to the right of the 'left-shift'
value except when switching modes.

(The 'left-shift' support is a bit of an overkill for this driver since
the trigger only has 16 input channels.)

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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