doc: provide a correct board_init_r definition path

This is a trivial fix in the documentation, which corrects
board_init_r() source reference.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>

doc/README.console

@@ -74,7 +74,7 @@ You can use the following functions to access the console:
     fgetc	(like getc but redirected to a file)
 
 Remember that all FILE-related functions CANNOT be used before
-U-Boot relocation (done in 'board_init_r' in common/board.c).
+U-Boot relocation (done in 'board_init_r' in arch/*/lib/board.c).
 
 HOW CAN I USE STANDARD FILE INTO APPLICATIONS?
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