soc: qcom: glink_smem_native_xprt: Fix blocked command handling

Commands which cannot be transmitted immediately due to a full fifo are
blocked until there is available space.  However the wait condition is
inverted which could cause a blocked command to be held forever.  Also, if
there is some room in the fifo, but not enough, the blocked command may
be stuck forever since the "flush" signal may not be retriggered.

Fix the handling of blocked commands by moving the responsibility entirely
to the blocked command so that corner cases do not result in stalls.

Change-Id: Id6b54f9129b6a115582ae0ce9130d940b213f8f7
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>