fmt: fix formatting of C.f(/*mut*/buff &char) i64 (#19069)

vlib/v/fmt/tests/c_fn_headers_with_comments_expected.vv

@@ -0,0 +1,7 @@
+module main
+
+fn main() {
+	println('Hello World!')
+}
+
+fn C.f( /* mut */ buff &char) i64

vlib/v/fmt/tests/c_fn_headers_with_comments_input.vv

@@ -0,0 +1,7 @@
+module main
+
+fn main() {
+	println('Hello World!')
+}
+
+fn C.f(/*mut*/buff &char) i64

vlib/v/parser/fn.v

@@ -948,6 +948,7 @@ fn (mut p Parser) fn_params() ([]ast.Param, bool, bool) {
 				is_mut: is_mut
 				typ: param_type
 				type_pos: type_pos
+				comments: comments
 			}
 			param_no++
 			if param_no > 1024 {