Is Atheros AR6102 all I need for my Wi-Fi SD card reader?
Out of the box, the chip is going to do nothing.  You're going to have to write software to run on the AR6102 that will interface with the WiFi radio and with the SD card interface.  Before buying a bunch of the chips, I would recommend buying a development board and familiarizing yourself with the development environment and libraries.  It's possible you will have to buy a license for the development software; I am not familiar with Qualcomm's way of doing things.  There may be some example code that you can look at that will help you get the interfaces operational.  Then you can define whatever protocol you want and implement it on both the AR6102 and in your app.  

One thing you might want to take note of: it seems that the SDIO interface on the controller is designed to go into an SD card slot as a card to interface with a host.  It looks like you may not be able to turn the link around to interface with an external SD card as the clock line seems to be input only.