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/board/freescale/m54455evb/README b/board/freescale/m54455evb/README
index 260aec9..26d3cc8 100644
--- a/board/freescale/m54455evb/README
+++ b/board/freescale/m54455evb/README
@@ -26,7 +26,7 @@
 - arch/m68k/cpu/mcf5445x/config.mk	config make
 - arch/m68k/cpu/mcf5445x/start.S		start up assembly code
 
-- doc/README.m54455evb	This readme file
+- board/freescale/m54455evb/README	This readme file
 
 - drivers/net/mcffec.c		ColdFire common FEC driver
 - drivers/serial/mcfuart.c	ColdFire common UART driver