staging: comedi: ni_at_ao: fix namespace clash of 'RSI' define

As pointed out by Fengguang Wu, the RSI define in this driver clashes
with the one in arch/x86/include/uapi/asm/ptrace-abi.h.

This define isn't currently used by the driver so just rename it to fix
the clash.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>