wifi: ath10k: drop fw.eboard file name

Follow the example set up by previous commit and drop .fw.eboard
setting. Instead always use "eboard.bin" in this case. QCA9984 already
uses that file name, any (im)possible future users will just have to use
the same file name.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240130-wcn3990-board-fw-v1-3-738f7c19a8c8@linaro.org