USB: dwc2: drop irq-flags initialisations

There's no need to initialise irq-flags variables before saving the
interrupt state.

While at it drop two redundant return-value initialisations from two of
the functions that got it wrong.

Cc: Minas Harutyunyan <hminas@synopsys.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210519093303.10789-3-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>