spi: stm32: Don't warn about spurious interrupts

The dev_warn to notify about a spurious interrupt was introduced with
the reasoning that these are unexpected. However spurious interrupts
tend to trigger continously and the error message on the serial console
prevents that the core's detection of spurious interrupts kicks in
(which disables the irq) and just floods the console.

Fixes: c64e7efe

 ("spi: stm32: make spurious and overrun interrupts visible")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://msgid.link/r/20240521105241.62400-2-u.kleine-koenig@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>