Bowed Stud at Rough Opening Door Frame
I can think of two potential fixes. In both cases, I wouldn't plane the stud at all, that compromises strength. 

Plane the jamb

Door jambs are typically 5/8" or 11/16". In this case, I would just use a planer on the center of the jamb to shave it down to the 1/2" needed. There'd obviously be no shims in the center. 

Fix the stud

If your drywall is not yet finished, and you a certain that the stud was not bowed before, you can try forcing it to be straight.

Pull all the screws out of the bowed stud. Cut a 2x4 to exactly 32", then use a hammer to wedge it in horizontally in the center of the door, pushing the stud straight again. 

Put several drywall screws back in place -- it's going to be the drywall that holds the stud from bowing again, so you need to make sure the connection is good. 

I'm definitely hesitant to suggest this, since if it doesn't work you'll end up with the edge of the drywall ripped apart by the screws holding it in, and if it gives way at some point after the construction is done, then you'll have a stuck door to contend with as well. You'll have to use your judgement to see if this is an appropriate fix.