mips: fix printing of invalid operations argument of sysmips syscall

* sysmips.c (SYS_FUNC(sysmips)): Print 1st argument of syscall using
printxval_long.
diff --git a/sysmips.c b/sysmips.c
index 10b102a..bc3cb8d 100644
--- a/sysmips.c
+++ b/sysmips.c
@@ -45,7 +45,7 @@
 
 SYS_FUNC(sysmips)
 {
-	printxval(sysmips_operations, tcp->u_arg[0], "???");
+	printxval_long(sysmips_operations, tcp->u_arg[0], "???");
 	tprints(", ");
 
 	switch (tcp->u_arg[0]) {