ksmbd: replace one-element arrays with flexible-array members

ksmbd: replace one-element arrays with flexible-array members

One-element arrays are deprecated, and we are replacing them with flexible
array members instead. So, replace one-element arrays with flexible-array
members in multiple structs in fs/ksmbd/smb_common.h and one in
fs/ksmbd/smb2pdu.h.

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/242
Link: https://github.com/KSPP/linux/issues/79
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/Y3OxronfaPYv9qGP@work