sign-file: fix the perl warning message when extracting ASN.1

There have the following warning message when running modules install
for sign ko files:

  # make modules_install
  ...
    INSTALL drivers/input/touchscreen/pcap_ts.ko
  Found = in conditional, should be == at scripts/sign-file line 164.
  Found = in conditional, should be == at scripts/sign-file line 161.
  Found = in conditional, should be == at scripts/sign-file line 159.

This patch change replace '=' by '==' in elsif conditions for avoid the
above warning messages.
Signed-off-by: Chun-Yi Lee <jlee@suse.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/sign-file

@@ -156,12 +156,12 @@ sub asn1_extract($$@)
 
 	if ($l == 0x1) {
 	    $len = unpack("C", substr(${$cursor->[2]}, $cursor->[0], 1));
-	} elsif ($l = 0x2) {
+	} elsif ($l == 0x2) {
 	    $len = unpack("n", substr(${$cursor->[2]}, $cursor->[0], 2));
-	} elsif ($l = 0x3) {
+	} elsif ($l == 0x3) {
 	    $len = unpack("C", substr(${$cursor->[2]}, $cursor->[0], 1)) << 16;
 	    $len = unpack("n", substr(${$cursor->[2]}, $cursor->[0] + 1, 2));
-	} elsif ($l = 0x4) {
+	} elsif ($l == 0x4) {
 	    $len = unpack("N", substr(${$cursor->[2]}, $cursor->[0], 4));
 	} else {
 	    die $x509, ": ", $cursor->[0], ": ASN.1 element too long (", $l, ")\n";