rockchip: fix stack overflow in rk8xx_rtc

Presumably surfaced by -fstack-protector-strong, rk8xx_settime was
triggering SSP when ntpd set the time on the RockPro64, at the very
least. A minor oops meant that the weeks mask was getting tossed into
the wrong field, and the mask was never populated. The mask is 0x7 for
all three of these, thus overflowing the data array in settime by one
byte.

PR: 296719
Reported by: jsm, "Tenkawa" on Discord
Reviewed by: mmel
Differential Revision: https://reviews.freebsd.org/D58182