wifi: ath10k: Drop checks that are always false

platform_get_drvdata() cannot return NULL as the probe function calls
platform_set_drvdata() with a non-NULL argument or returns with a failure.
In the first case, platform_get_drvdata() returns this non-NULL value and
in the second the remove callback isn't called at all.

ath10k_ahb_priv() cannot return NULL and ar_ahb is unused after the check
anyhow.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230601082556.2738446-3-u.kleine-koenig@pengutronix.de