usb: musb: Call pm_runtime from musb_gadget_queue

If we're booting pandaboard using NFSroot over built-in g_ether, we
can get the following after booting once and doing a warm reset:

g_ether gadget: ecm_open
g_ether gadget: notify connect true
...
WARNING: CPU: 0 PID: 1 at drivers/bus/omap_l3_noc.c:147
l3_interrupt_handler+0x220/0x34c
44000000.ocp:L3 Custom Error: MASTER MPU TARGET L4CFG (Read):
Data Access in User mode du ring Functional access
...

Fix the issue by calling pm_runtime functions from
musb_gadget_queue.

Note that in the long run we should be able to queue the pending
transfers if pm_runtime is not active, and flush the queue from
pm_runtime_resume.

Reported-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>