mhi: core: Fix find_last_bit() usage

BugLink: https://bugs.launchpad.net/bugs/1940100



find_last_bit() relies on unsigned long pointer arguments. Driver
uses a type cast that generates the KASAN warning. Replace
find_last_bit() with __fls() to pass the value and avoid casting
pointer to make the warning go away.

Change-Id: I247e5c425ba0c44d04b518bd6d4f351f9c700b29
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
(cherry picked from commit 571e9c8d6a4ac708aac0fad3e6d751d402cb4ae9)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>