doc: update reference to README.board

Update reference in files detected by
scripts/documentation-file-ref-check

doc/README.<board>  => board/<board>/README

Files moved in board directory in
commit 702e6014f15b ("doc: cleanup - move board
READMEs into respective board directories")'

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/include/configs/sbc8548.h b/include/configs/sbc8548.h
index f4113e0..ae2c003 100644
--- a/include/configs/sbc8548.h
+++ b/include/configs/sbc8548.h
@@ -7,7 +7,7 @@
 
 /*
  * sbc8548 board configuration file
- * Please refer to doc/README.sbc8548 for more info.
+ * Please refer to board/sbc8548/README for more info.
  */
 #ifndef __CONFIG_H
 #define __CONFIG_H