wifi: wil6210: fix sparse warnings

Sparse warns:

drivers/net/wireless/ath/wil6210/fw.c: note: in included file (through drivers/net/wireless/ath/wil6210/wil6210.h):
drivers/net/wireless/ath/wil6210/fw.h:96:47: warning: array of flexible structures
drivers/net/wireless/ath/wil6210/cfg80211.c: note: in included file (through drivers/net/wireless/ath/wil6210/wil6210.h):
drivers/net/wireless/ath/wil6210/fw.h:96:47: warning: array of flexible structures

I decided to remove the combos field altogether and just do pointer arithmetic
instead. Not pretty but I didn't want to waste too much time on an orphaned
driver.

Compile tested only.

Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240320182449.3757215-5-kvalo@kernel.org