staging: comedi: s626: remove TRUE and FALSE macros

"s626.h" defines the macros `TRUE` and `FALSE` if they are not already
defined, yielding the expected numeric values.  Remove the macros and
replace their usage with the values `true` and `false`, respectively.

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>