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>
1 file changed