spi: amlogic: fix spifc build error

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: 4670db6f32e9 ("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>