arm's fls() is implemented as a macro, causing it to misbehave when passed
64-bit arguments.  Fix.

Cc: Nickolay Vinogradov <nickolay@protei.ru>
Tested-by: NKrzysztof Halasa <khc@pm.waw.pl>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>