ath10k: use devm_reset_control_get() instead of reset_control_get()

Use the managed variant of reset_control_get() to simplify the
failure path and the .remove callback.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>