pkg(7): address minor nits (mostly clang-analyze complaints)

- One (1) spurious whitespace.
- One (1) occurrence of "random(3) bad, arc4random(3)" good.
- Three (3) writes that will never be seen.

The latter two points are complaints from clang-analyze. Switching to
arc4random(3) is decidedly a good idea because we weren't doing any kind
of PRNG seeding anyways. The discarded assignments are arguably good
for future-proofing, but it's better to improve the S/N ratio from
clang-analyze.

Reviewed by:	bapt, manu
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D28525

usr.sbin/pkg/dns_utils.c

@@ -98,7 +98,8 @@ compute_weight(struct dns_srvinfo **d, int first, int last)
 
 	for (i = 0; i <= last; i++) {
 		for (;;) {
-			chosen[i] = random() % (d[i]->weight * 100 / totalweight);
+			chosen[i] = arc4random_uniform(d[i]->weight * 100 /
+			    totalweight);
 			for (j = 0; j < i; j++) {
 				if (chosen[i] == chosen[j])
 					break;

usr.sbin/pkg/pkg.c

@@ -434,9 +434,7 @@ sha256_fd(int fd, char out[SHA256_DIGEST_LENGTH * 2 + 1])
 	int ret;
 	SHA256_CTX sha256;
 
-	my_fd = -1;
 	fp = NULL;
-	r = 0;
 	ret = 1;
 
 	out[0] = '\0';
@@ -627,7 +625,6 @@ parse_cert(int fd) {
 	ssize_t linelen;
 
 	buf = NULL;
-	my_fd = -1;
 	sc = NULL;
 	line = NULL;
 	linecap = 0;