ath10k: different fw file name for sdio

Since both SDIO based chipsets will use different
firmware from the PCIe and AHB chipsets, the fw file name
must be different depending on bus type.

The new firmware names are:

For PCIe and AHB:
firmware-<api_version>.bin (same as before)

For SDIO:
firmware-sdio-<api_version>.bin

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>