No, the radios aren't 100% efficient, so you can't assume that. If this is a Pegatron WL-266N22-Duband, it might draw considerably more (based on the hardware it contains; I don't have any specific data though).
I recommend you try with an AMS1117 linear regulator, but use an USB power meter (cheapie off fleabay) to verify the actual USB power consumption. The point is, you shouldn't assume you can draw more than 500mA off USB +5V, and you can use a cheapie USB power meter to check that.
There have been WiFi USB sticks that draw more than 500mA, and won't work on all machines. Desktop and laptop PC's often can supply quite a bit more current, so they do work on most of those, but when you have a machine that actually follows the USB standard (say, a low-powered single-board computer), they don't work anymore. Or even crash the machine, by drawing too much current off the +5V line, sagging it too much. It is horrible to debug, too, unless you know to suspect the power consumption.