wl12xx: fix the path to the wl12xx firmwares

In the linux-firmware git tree, the firmwares and the NVS are inside
the ti-connectivity directory.  Fix the filenames that the driver
looks for accordingly.

[Fixed commit message and merged with the latest changes. -- Luca]

Signed-off-by: Sebastien Jan <s-jan@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>