WCN3990 supports shadow registers write operation support
for copy engine for regular operation in powersave mode.

Since WCN3990 is a 64-bit target, the shadow register
implementation needs to be done in the copy engine handlers
for 64-bit target. Currently the shadow register implementation
is present in the 32-bit target handlers of copy engine.

Fix the shadow register copy engine write operation
implementation for 64-bit target(WCN3990).

Tested HW: WCN3990
Tested FW: WLAN.HL.2.0-01188-QCAHLSWMTPLZ-1

Fixes: b7ba83f7 ("ath10k: add support for shadow register for WNC3990")
Signed-off-by: Rakesh Pillai <pillair@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>