ipa: Fix to MHI channel state update

Make a change to use the right channel state size when
updating the state info to avoid overwriting other fields
in the MHI context.

Change-Id: Ic0483dedaacfd3d74452f561b4e25953a1e24fb0
Acked-by: Chaitanya Pratapa <cpratapa@qti.qualcomm.com>
Signed-off-by: Mohammed Javid <mjavid@codeaurora.org>