embed.fnc: Use correct name for formal parameter

The prototype here did not match the actual function

Author: khwilliamson

embed.fnc

@@ -3124,7 +3124,7 @@ Adp	|NV	|scan_bin	|NN const char *start			\
 Adp	|NV	|scan_hex	|NN const char *start			\
 				|STRLEN len				\
 				|NN STRLEN *retlen
-Cp	|char * |scan_num	|NN const char *s			\
+Cp	|char * |scan_num	|NN const char *start			\
 				|NN YYSTYPE *lvalp
 Adp	|NV	|scan_oct	|NN const char *start			\
 				|STRLEN len				\