lib/div64.c: off by one in shift

lib/div64.c: off by one in shift

BugLink: https://bugs.launchpad.net/bugs/1838349
[ Upstream commit cdc94a37493135e355dfc0b0e086d84e3eadb50d ]

fls counts bits starting from 1 to 32 (returns 0 for zero argument).  If
we add 1 we shift right one bit more and loose precision from divisor,
what cause function incorect results with some numbers.

Corrected code was tested in user-space, see bugzilla:
   https://bugzilla.kernel.org/show_bug.cgi?id=202391

Link: http://lkml.kernel.org/r/1548686944-11891-1-git-send-email-sgruszka@redhat.com
Fixes: 658716d19f8f ("div64_u64(): improve precision on 32bit platforms")
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Reported-by: Siarhei Volkau <lis8215@gmail.com>
Tested-by: Siarhei Volkau <lis8215@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>