spi: dw: fix wrong BAUDR setting after resume

[ Upstream commit 66b6605 ]

After resuming from suspend to ram, spi transfer stops working. Further
debugging shows that the BAUDR register isn't correctly set, this is
due to dws->current_freq doesn't match the HW BAUDR setting,
specifically, the dws->current_freq equals to speed_hz, but BAUDR is 0.
so the dw_spi_set_clk() in below code won't be called:

        if (dws->current_freq != speed_hz) {
                dw_spi_set_clk(dws, clk_div);
                dws->current_freq = speed_hz;
        }

The mismatch comes from dw_spi_shutdown_chip() when suspending.
Fix this mismatch by setting dws->current_freq to 0 as well when
clearing BAUDR reg in dw_spi_shutdown_chip().

Fixes: e24c745 ("spi: controller driver for Designware SPI core")
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://patch.msgid.link/20260612002835.5240-1-jszhang@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: xhackerustc

drivers/spi/spi-dw.h

@@ -282,6 +282,7 @@ static inline void dw_spi_shutdown_chip(struct dw_spi *dws)
 {
 	dw_spi_enable_chip(dws, 0);
 	dw_spi_set_clk(dws, 0);
+	dws->current_freq = 0;
 }
 
 extern void dw_spi_set_cs(struct spi_device *spi, bool enable);