wifi: ath10k: remove unused ath10k_get_ring_byte function

clang with W=1 reports:

drivers/net/wireless/ath/ath10k/ce.c:88:1: error:
  unused function 'ath10k_get_ring_byte' [-Werror,-Wunused-function]
ath10k_get_ring_byte(unsigned int offset,
^
This function is not used so remove it.

Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230322122855.2570417-1-trix@redhat.com