Hi Macro,
Your actual firmware file (wl18xx-fw-mc.bin) is either missing or placed in an incorrect directory. Are you able to locate where your firmware file is?
When you build the WL8 driver by executing the build script, you should already have the /lib/firmware/ti-connectivity directory created and wl18xx-fw-mc.bin firmware file inside. Please make sure it is there, or otherwise something is wrong during your building.
As a reference, the following is my directory on AM335X:
root@am335x-evm:/lib/firmware/ti-connectivity# ls
Android.mk wl128x-fw-4-plt.bin
LICENCE wl128x-fw-4-sr.bin
wl1271-fw-multirole-plt.bin wl128x-fw-multirole-plt.bin
wl1271-fw-multirole-roc.bin wl128x-fw-multirole-roc.bin
wl1271-nvs.bin wl18xx-conf.bin
wl127x-fw-4-mr.bin wl18xx-fw-mc.bin
wl127x-fw-4-plt.bin wl18xx-fw-pg1.1.bin
wl127x-fw-4-sr.bin wl18xx-fw.bin
wl128x-fw-4-mr.bin