spi: amlogic: fix spifc build error

There is an error building when
Compiler version: gcc (GCC) 14.3.0
Assembler version: GNU assembler (GNU Binutils) 2.44
"
 Error log:
 WARNING: modpost: missing MODULE_DESCRIPTION() in arch/arm/probes/kprobes/test-kprobes.o
 ERROR: modpost: "__ffsdi2" [drivers/spi/spi-amlogic-spifc-a4.ko] undefined!
"

Use __ffs API instead of __bf_shf to be safer.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/all/f594c621-f9e1-49f2-af31-23fbcb176058@roeck-us.net/
Fixes: 4670db6 ("spi: amlogic: add driver for Amlogic SPI Flash Controller")
Signed-off-by: Xianwei Zhao <xianwei.zhao@amlogic.com>
Link: https://patch.msgid.link/20251015-fix-spifc-a4-v1-1-08e0900e5b7e@amlogic.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Xianwei Zhao

drivers/spi/spi-amlogic-spifc-a4.c

@@ -286,7 +286,7 @@ static int aml_sfc_set_bus_width(struct aml_sfc *sfc, u8 buswidth, u32 mask)
 
 	for (i = 0; i <= LANE_MAX; i++) {
 		if (buswidth == 1 << i) {
-			conf = i << __bf_shf(mask);
+			conf = i << __ffs(mask);
 			return regmap_update_bits(sfc->regmap_base, SFC_SPI_CFG,
 						  mask, conf);
 		}
@@ -566,7 +566,7 @@ static int aml_sfc_raw_io_op(struct aml_sfc *sfc, const struct spi_mem_op *op)
 	if (!op->data.nbytes)
 		goto end_xfer;
 
-	conf = (op->data.nbytes >> RAW_SIZE_BW) << __bf_shf(RAW_EXT_SIZE);
+	conf = (op->data.nbytes >> RAW_SIZE_BW) << __ffs(RAW_EXT_SIZE);
 	ret = regmap_update_bits(sfc->regmap_base, SFC_SPI_CFG, RAW_EXT_SIZE, conf);
 	if (ret)
 		goto err_out;