lms: Fix stream_stats checks with droppedPackets

Existing code had a typo (value was assigned from wrong variable).
Furthermore, it was experimentally found that:
while underrun/overrun are documented as "FIFO overrun
count" in LimeSuite.h, it seems droppedPackets ("Number of dropped
packets by HW") is not actually an incrementing counter like the others,
but simply a value set every time LMS_RecvStream() is called. Since we
are actually interested in keeping the count over time, adjust code to
achieve that.

Change-Id: Id93d33400e11360b9536f56a31904328549cfbbf
1 file changed