Can I replace my broken GFCI outlet with a single outlet with 2 USB ports?
This GFCI probably has downstream outlets.

They probably were protected by the GFCI, up until the point the GFCI blew.  They will now be dead.   

If any of them are in a garage, basement, laundry room, or pretty much any room containing a sink, those outlets need to still be GFCI.   So you will need to provide for their protection. 

You can't defeat the GFCI ...probably.  As said, you can't break GFCI protection for any outlet that needs to be protected. 

No such thing as a GFCI USB ... Yet.

The market doesn't appear to make what you want, a GFCI receptacle with a USB outlet also.   I could be wrong, if you've found one, carry on.   In the meantime, I'll talk about the workarounds in case you can't find one. 

Install the GFCI protection upstream.

Follow the circuit in the other direction, back toward the circuit breaker.  These are outlets that are still working... but lose power when you turn off the breaker for this circuit.  Are there GFCI receptacles in any of those?  Is the breaker itself a GFCI?  Then you're all set.  If it's not that way, buy a GFCI outlet or breaker and  make it so. 

You only need one GFCI and it will protect all the outlets downstream of it, provided those are connected to the LOAD side of the GFCI.  Some people daisy-chain GFCI's, that is redundant.  

Now you can install your USB outlet (which does not have GFCI).   

If you can't do the above, then replace the GFCI the way you found it, and put the USB outlet somewhere else.