msm: mhi_dev: Do not free channel memory in mhi_deinit

The channel memory may still be referenced when a client calls
mhi_dev_close_channel as part of clean-up when a channel
disconnect notification is sent.

Change-Id: I2dd73efce5186667cf76cf0da3e4f746b0cc8bba
Signed-off-by: Siva Kumar Akkireddi <sivaa@codeaurora.org>