So the 4.60 firmware update bricked my PS3
Hello, the 4.60 firmware update was a very minor update, it is odd that it should have 'bricked' your console (unless it was a coincidence and the console fault is not attributable to the update).
The saves that are on the USB may now be unreadable by the console due to a console interface fault. You can check if the USB saves have been corrupted by trying them in another PS3 unit. Either a friend who also plays GTA V on PS3 may be able to help, or failing that, a games store will check the save data for you.
If the save files can be read and loaded by another console, they can be read by any console apart from yours which is faulty.
Your next option then will be to decide whether to have your console repaired or buy a second hand (working) console and continue your game using the USB saves, or wait until the game comes out on PS4 and start again.
If the save data cannot be read from the USB drive by another console, the data is indeed damaged and unfortunately you will have to go back to square one.