staging: comedi: usbduxsigma: tidy up usbdux_ai_insn_read()
staging: comedi: usbduxsigma: tidy up usbdux_ai_insn_read()

Rename the function so it has namespace associated with the driver.
Rename the local variable used for the private data pointer.

Return -EBUSY if an asynchronous command is running and the read cannot
be completed.

Propagate the errno if the receive_dux_command() fails.

Tidy up the function to make it more concise.

Signed-off-by: H Hartley Sweeten <382ff55d8e07d1082d179e669636cd1552da4f36@visionengravers.com>
Cc: Ian Abbott <9e6ba6483b6a3e14d61f7c987e72ecb5b46122d6@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs