staging: comedi: s626: clock polarity and direction are the same

When setting up an encoder channel, the setup value includes a polarity
and direction, but these are the same bit of the setup value:

  S626_CLKPOL_POS = S626_CNTDIR_UP = 0

  S626_CLKPOL_NEG = S626_CNTDIR_DOWN = 1

In the construction of the setup value, both the CLKPOL and the CNTDIR
constants are shifted by the same amount `S626_BF_CLKPOL`.  Only the
following combinations are set up currently (this may change if user
configuration of the encoder is implemented properly):

  (S626_CLKPOL_POS << S626_BF_CLKPOL)

  (S626_CLKPOL_POS << S626_BF_CLKPOL) |
  (S626_CNTDIR_UP << S626_BF_CLKPOL)

  (S626_CLKPOL_POS << S626_BF_CLKPOL) |
  (S626_CNTDIR_DOWN << S626_BF_CLKPOL)

The first two are used in "counter" mode and is equivalent to:

  (S626_CLKPOL_POS << S626_BF_CLKPOL)

The last one is used in "timer" mode and is equivalent to:

  (S626_CNTDIR_DOWN << S626_BF_CLKPOL)

Use the shorter equivalents.  The comments in "s626.h" indicate that the
'CLKPOL' constants make more sense for the "counter" mode (when the
encoders operate as up/down counters) and the 'CNTDIR' constants make
more sense for the "timer" mode.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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