Fix compilation of sha256-armv4.S when using -march=armv6

sha256-armv4.S:1884: Error: invalid constant (ffffffffffffef90) after fixup

BUG=495695

Change-Id: I5b7423c2f7a10657c92c7b1ccae970f33c569455
Reviewed-on: https://boringssl-review.googlesource.com/4944
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/sha/asm/sha256-armv4.pl b/crypto/sha/asm/sha256-armv4.pl
index 778c3d9..df71676 100644
--- a/crypto/sha/asm/sha256-armv4.pl
+++ b/crypto/sha/asm/sha256-armv4.pl
@@ -479,7 +479,7 @@
 	stmdb	sp!,{r4-r12,lr}
 
 	sub	$H,sp,#16*4+16
-	adr	$Ktbl,K256
+	adrl	$Ktbl,K256
 	bic	$H,$H,#15		@ align for 128-bit stores
 	mov	$t2,sp
 	mov	sp,$H			@ alloca