bus: mhi: host: Drop chan lock before queuing buffers

In the Linux kernel, the following vulnerability has been resolved:

bus: mhi: host: Drop chan lock before queuing buffers

Ensure read and write locks for the channel are not taken in succession by

dropping the read lock from parse_xfer_event() such that a callback given

to client can potentially queue buffers and acquire the write lock in that

process. Any queueing of buffers should be done without channel read lock

acquired as it can result in multiple locks and a soft lockup.

[mani: added fixes tag and cc'ed stable]