util/ra: Fix numeric overflow during bitset allocation

Fixes this issue. The problem was the big number of registers (>100000). In this case unsigned is not enough to handle the number of bits required for adjacency bits count.

CC: @tpalli
Reviewed-by: Emma Anholt emma@anholt.net
Signed-off-by: Kostiantyn Lazukin kostiantyn.lazukin@globallogic.com
Closes: #5752 (closed)
Fixes: d4a4cd20 ("util/ra: use adjacency matrix for undirected graph")