Though it seems obvious, it is indeed a tricky business, as buses Malaga to Torremolinos depart from a different location than the main Bus Station. They depart from Muelle Heredia, very near the harbour entrance, a moderate walk from the main Station. Then, Carihuela is not in Torremolinos, but down on the beach, past Torremolinos, and it is a long stretch (you'd have to check the place you are going, or you may end up walking again). I'll try to phone the bus company (Portillo) tomorrow, to find out, but it looks your best option is taking a taxi.

There is no bus to Torremolinos departing from Malaga Bus Station (where you arrive from Granada) as the buses to/from Torremolinos depart from Muelle Heredia. However, this is not a direct bus and it stops along the way, one of them in the Railway Station, which is next door to the Bus Station.
So, exit the Estacion de Autobuses and turn left, and then left again (heading south), a short walk to Railway Station Maria Zambrano, better known as Vialia (which is the name of the shopping mall in there). The bus is Portillo number 110, the stop is at the entrance on Calle Heroes de Sostoa. Check a map.