usb: mdm_ctrl_bridge: Do not unlink URB upon cable disconnect

MDM control bridge driver unlinks the pending URBs when control
bridge gets closed as a result of usb cable disconnect. Driver
sends set_control_line_state request to MDM upon bridge close.
Right after sending the setup request driver unlinks the pending
URBs. In case if the URB is unlinked after setup stage is completed,
status stage remains pending. This results in a control transfer
stall. Similarly, when the bridge is reopened as a result of USB
cable plug-in, the interrupt URB is not resubmitted, which can also
lead to a QMI stall since the MDM is waiting indefinitely to send
its response available notification. Fix these two potential stall
conditions by not unlinking URBs upon cable disconnect; this will
allow in-progress control transfers to finish gracefully and will
also allow notification interrupts to always be handled. Unlinking
of the URBs will happen during MDM device disconnect, instead of
upon bridge close.

(cherry picked from commit 77f79575ebe35f2ec329827290e7a67fb0e75286)
CRs-Fixed: 419128,418478

Change-Id: I5474372d832de2fd49f17faf77e7e549e80566ad
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Neha Pandey <nehap@codeaurora.org>