IB/uverbs: Prevent reregistration of DM_MR to regular MR

This patch adds a check in the ib_uverbs_rereg_mr flow to make
sure there's no attempt to rereg a device memory MR to regular MR.
In such case the command will fail with -EINVAL status.

fixes: be934cca ("IB/uverbs: Add device memory registration ioctl support")
Signed-off-by: Ariel Levkovich <lariel@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>