ral: rt2860: fix wcid2ni access/size issue

RT2860_WCID_MAX is supposed to describe the max STA index for wcid2ni, and
was instead being used as the size -- off-by-one.

rt2860_drain_stats_fifo was range-checking wcid only after accessing
out-of-bounds potentially.

Submitted by: Augustin Cavalier <waddlesplash@gmail.com> (basically)
Obtained from: Haiku (58d16d9fe2d5a209cf22823359a8407d138e1a87)
Differential Revision: 3 days