usb: dwc2: Get rid of useless error checks in suspend interrupt

Squashed from Douglas Anderson's suggested commit
"usb: dwc2: Get rid of useless error checks for
hibernation/partial power down"

 - After this commit there should never be any
case where dwc2_enter_partial_power_down() and
dwc2_enter_hibernation() are called when
'params.power_down' is not correct.  Get rid of
the pile of error checking.

- As part of this cleanup some of the error messages
not to have __func__ in them.  That's not needed
for dev_err() calls since they already have the
device name as part of the message.

Acked-by: Minas Harutyunyan <Minas.Harutyunyan@synopsys.com>
Signed-off-by: Artur Petrosyan <Arthur.Petrosyan@synopsys.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20210416124843.9EDCDA005D@mailhost.synopsys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>