Input: ads7877 - remove bitrotted comment

While searching for users of spi_async() I found a reference in the ad7877
driver to using it to initiate data transfer from the interrupt handler.
However there is no code for this, instead the interrupt handler is a
threaded handler and uses spi_sync() instead.

Remove the bitrotted comment, though in actual fact the use case mentioned
is a great use for spi_async() since it would cut down on latency handling
the interrupt by saving us a context switch before we start SPI.

This was previously implemented, it was removed in commit b534422b2d11
(Input: ad7877 - switch to using threaded IRQ) for code complexity reasons.
It may be better to revert that commit instead.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/ad7877.c

@@ -210,11 +210,6 @@ static bool gpio3;
 module_param(gpio3, bool, 0);
 MODULE_PARM_DESC(gpio3, "If gpio3 is set to 1 AUX3 acts as GPIO3");
 
-/*
- * ad7877_read/write are only used for initial setup and for sysfs controls.
- * The main traffic is done using spi_async() in the interrupt handler.
- */
-
 static int ad7877_read(struct spi_device *spi, u16 reg)
 {
 	struct ser_req *req;