wifi: brcmfmac: Use struct_size() and array_size() in code ralated to struct brcmf_gscan_config

Prefer struct_size() over open-coded versions of idiom:

sizeof(struct-with-flex-array) + sizeof(typeof-flex-array-elements) * count

where count is the max number of items the flexible array is supposed to
contain.

Also, use array_size() in call to memcpy().

Link: https://github.com/KSPP/linux/issues/160
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/de0226a549c8d000d8974e207ede786220a3df1a.1668466470.git.gustavoars@kernel.org