usb: musb: musb_dsps: request_irq() after initializing musb

If IRQ occurs between calling  dsps_setup_optional_vbus_irq()
and  dsps_create_musb_pdev(), then null pointer dereference occurs
since glue->musb wasn't initialized yet.

The patch puts initializing of neccesery data before registration
of the interrupt handler.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Nadezda Lutovinova <lutovinova@ispras.ru>
Link: https://lore.kernel.org/r/20210819163323.17714-1-lutovinova@ispras.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>