arm: dts: ls1028a-qds: use Linux compatible string for RTC

The LS1028A-QDS board won't be synced with the Linux device trees right
now, since those are currently still in progress (Ethernet is missing).

However, while we're at converting the RDB, it can be observed that the
same RTC is present on the two boards, and the wrong compatible string
is used in both places. This change updates the RTC from the QDS to use
the compatible string that was established in Linux.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
Reviewed-by: Michael Walle <michael@walle.cc>