UPSTREAM: ARM: 8564/1: fix cpu feature extracting helper

Commit b8c9592 "ARM: 8318/1: treat CPU feature register fields as signed
quantities" introduced helper to extract signed quantities of 4-bit
blocks. However, with a current code feature with value 0b1000 isn't
rejected as negative. So fix the "if" condition.

Reported-by: Jonathan Brawn <Jon.Brawn@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
(cherry picked from commit ac36a881b72a1e9831f1c59abf935868c90685cf)
Change-Id: I7745736681331f8f18740675044612ad538c2ce3
Signed-off-by: Eric Biggers <ebiggers@google.com>