block-backend: Silence clang -m32 compiler warning

block-backend: Silence clang -m32 compiler warning

Similarly to e7e588d432d31ecebc26358e47201dd108db964c, there is a
warning in block/block-backend.c that qiov->size <= INT64_MAX is always
true on machines where size_t is narrower than a uint64_t.  In said
commit, we silenced this warning by casting to uint64_t.

The commit introducing this warning here
(a93d81c84afa717b0a1a6947524d8d1fbfd6bbf5) anticipated it and so tried
to address it the same way.  However, it only did so in one of two
places where this comparison occurs, and so we still need to fix up the
other one.

Fixes: a93d81c84afa717b0a1a6947524d8d1fbfd6bbf5
       ("block-backend: convert blk_aio_ functions to int64_t bytes
       paramter")
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20211026090745.30800-1-hreitz@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>