PF mcam entries has to be at low priority always so that VF
can install longest prefix match rules at higher priority.
This was taken care currently but when priority allocation
wrt reference entry is requested then entries are allocated
from mid-zone instead of low priority zone. Fix this and
always allocate entries from low priority zone for PFs.

Fixes: 7df5b4b2 ("octeontx2-af: Allocate low priority entries for PF")
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>