diag: Remove memory device entries while mhi disconnect

When mhi remove call on diag channels is issued clear memory
device table entries including buffer information to prevent
any race condition of using the buffers queued for copying
to diag userspace clients.

Change-Id: Ie311c63c5fce31e43d7c93c23f27cfe0e2e2d64f
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>