Staging: comedi: amplc_pc236: Corrected documentation.

Interrupt is triggered by rising edge on port C bit 3 (not bit 7).

From: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>