blk-wbt: fix old-style function declaration

The newly added driver causes a harmless warning in some configurations:

block/blk-wbt.c:250:1: error: ‘inline’ is not at beginning of declaration [-Werror=old-style-declaration]
 static bool inline stat_sample_valid(struct blk_rq_stat *stat)

This makes it use the expected format for the declaration.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-wbt.c

@@ -247,7 +247,7 @@ static bool calc_wb_limits(struct rq_wb *rwb)
 	return ret;
 }
 
-static bool inline stat_sample_valid(struct blk_rq_stat *stat)
+static inline bool stat_sample_valid(struct blk_rq_stat *stat)
 {
 	/*
 	 * We need at least one read sample, and a minimum of