ath10k: Fix the MTU size on QCA9377 SDIO

On an imx6dl-pico-pi board with a QCA9377 SDIO chip, simply trying to
connect via ssh to another machine causes:

[   55.824159] ath10k_sdio mmc1:0001:1: failed to transmit packet, dropping: -12
[   55.832169] ath10k_sdio mmc1:0001:1: failed to submit frame: -12
[   55.838529] ath10k_sdio mmc1:0001:1: failed to push frame: -12
[   55.905863] ath10k_sdio mmc1:0001:1: failed to transmit packet, dropping: -12
[   55.913650] ath10k_sdio mmc1:0001:1: failed to submit frame: -12
[   55.919887] ath10k_sdio mmc1:0001:1: failed to push frame: -12

, leading to an ssh connection failure.

One user inspected the size of frames on Wireshark and reported
the followig:

"I was able to narrow the issue down to the mtu. If I set the mtu for
the wlan0 device to 1486 instead of 1500, the issue does not happen.

The size of frames that I see on Wireshark is exactly 1500 after
setting it to 1486."

Clearing the HI_ACS_FLAGS_ALT_DATA_CREDIT_SIZE avoids the problem and
the ssh command works successfully after that.

Introduce a 'credit_size_workaround' field to ath10k_hw_params for
the QCA9377 SDIO, so that the HI_ACS_FLAGS_ALT_DATA_CREDIT_SIZE
is not set in this case.

Tested with QCA9377 SDIO with firmware WLAN.TF.1.1.1-00061-QCATFSWPZ-1.

Fixes: 2f918ea9

 ("ath10k: enable alt data of TX path for sdio")
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20211124131047.713756-1-festevam@denx.de