emp: fix warning on deprecated bison directive

emp_ematch.y:12.1-13: warning: deprecated directive, use ‘%name-prefix’ [-Wdeprecated]
 %name-prefix="ematch_"
 ^^^^^^^^^^^^^

tc/emp_ematch.y

@@ -9,7 +9,7 @@
 %locations
 %token-table
 %error-verbose
-%name-prefix="ematch_"
+%name-prefix "ematch_"
 
 %union {
 	unsigned int i;