dtc: move declaration of yyerror

yyerror() is used by both dtc-parser.y and dtc-lexer.l, so move
the declaration to srcpos.h.

Signed-off-by: Milton Miller <miltonm@bga.com>

dtc-parser.y

@@ -26,7 +26,6 @@
 #include "srcpos.h"
 
 int yylex(void);
-void yyerror(char const *);
 cell_t cell_from_string(char *s, unsigned int base);
 
 extern struct boot_info *the_boot_info;

srcpos.h

@@ -62,6 +62,7 @@ typedef struct YYLTYPE {
 
 
 
+extern void yyerror(char const *);
 
 extern int srcpos_filenum;