wifi: wcn36xx: buff_to_be(): fix sparse warnings

Sparse warns:

drivers/net/wireless/ath/wcn36xx/txrx.c: note: in included file (through drivers/net/wireless/ath/wcn36xx/txrx.h):
drivers/net/wireless/ath/wcn36xx/wcn36xx.h:107:24: warning: incorrect type in assignment (different base types)
drivers/net/wireless/ath/wcn36xx/wcn36xx.h:107:24:    expected unsigned int [usertype]
drivers/net/wireless/ath/wcn36xx/wcn36xx.h:107:24:    got restricted __be32 [usertype]
drivers/net/wireless/ath/wcn36xx/wcn36xx.h:107:24: warning: incorrect type in assignment (different base types)
drivers/net/wireless/ath/wcn36xx/wcn36xx.h:107:24:    expected unsigned int [usertype]
drivers/net/wireless/ath/wcn36xx/wcn36xx.h:107:24:    got restricted __be32 [usertype]

Use void pointers and two separate variables to workaround the warning. Also
now the callers don't need any casting. There's actually cpu_to_be32_array()
available but decided to do minimal changes instead.

Compile tested only.

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240320182449.3757215-3-kvalo@kernel.org