msm: mhi_dev: Process the PM_RST_DEAST event in the caller context

With the commit <37ea867103f2>("msm: ep-pcie: Use threaded irq for
PERST de-assertion handling"), PCIe driver notifies the PM_RST_DEAST
event in threadedIRQ context. Process this event in the same
context so that we can finish link initialization and training as
quickly as possible.

Change-Id: If920fd9b653d6ae82cea599effb2d912a9b08174
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>