msm: mhi: Queue channel db only if channel is open

Channel interrupts are seen on device even before,
channel ring is initialized. Queuing pending work
without checking ring status can lead to processing
of spurious interrupts. Adding proper checks in place
before queuing channel doorbell.

Change-Id: I3ccd7302b535d2b8ef63eada9d7a1fe553dccdaa
Signed-off-by: Nitesh Gupta <nitegupt@codeaurora.org>
Signed-off-by: Gauri Joshi <gaurjosh@codeaurora.org>