ath11k: Avoid memcpy() over-reading of he_cap

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring array fields.

Since peer_he_cap_{mac,phy}info and he_cap_elem.{mac,phy}_cap_info are not
the same sizes, memcpy() was reading beyond field boundaries. Instead,
correctly cap the copy length and pad out any difference in size
(peer_he_cap_macinfo is 8 bytes whereas mac_cap_info is 6, and
peer_he_cap_phyinfo is 12 bytes whereas phy_cap_info is 11).

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210616195410.1232119-1-keescook@chromium.org