ath10k: remove shadow copy of CE descriptors for source ring

For the messages from host to target, shadow copy of CE descriptors
are maintained in source ring. Before writing actual CE descriptor,
first shadow copy is filled and then it is copied to CE address space.
To optimize in download path and to reduce d-cache pressure, removing
shadow copy of CE descriptors. This will also reduce driver memory
consumption by 33KB during on device probing.

Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>