mm: split off __bdi_set_min_ratio() function

This splits off the __bdi_set_min_ratio() function from the
bdi_set_min_ratio() function. The __bdi_set_min_ratio() function will
also be called from the bdi_set_min_bytes() function, which will be
introduced in the next patch.

Link: https://lkml.kernel.org/r/20221119005215.3052436-12-shr@devkernel.ioSigned-off-by: NStefan Roesch <shr@devkernel.io>
Cc: Chris Mason <clm@meta.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

mm/page-writeback.c

@@ -685,7 +685,7 @@ static u64 bdi_get_bytes(unsigned int ratio)
 	return bytes;
 }
 
-int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
+static int __bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 {
 	unsigned int delta;
 	int ret = 0;
@@ -731,6 +731,11 @@ static int __bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ra
 	return ret;
 }
 
+int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
+{
+	return __bdi_set_min_ratio(bdi, min_ratio * BDI_RATIO_SCALE);
+}
+
 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio)
 {
 	if (max_ratio > 100)