wifi: brcmfmac: replace one-element array with flexible-array member in struct brcmf_dload_data_le

One-element arrays are deprecated, and we are replacing them with flexible
array members instead. So, replace one-element array with flexible-array
member in struct brcmf_dload_data_le.

Important to mention is that doing a build before/after this patch results
in no binary output differences.

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE routines
on memcpy() and help us make progress towards globally enabling
-fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/230
Link: https://github.com/KSPP/linux/issues/79
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
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/905f5b68cf93c812360d081caae5b15221db09b6.1668548907.git.gustavoars@kernel.org