min/max: remove sparse warnings when they're nested

min/max: remove sparse warnings when they're nested

Currently, when min/max are nested within themselves, sparse will warn:

    warning: symbol '_min1' shadows an earlier one
    originally declared here
    warning: symbol '_min1' shadows an earlier one
    originally declared here
    warning: symbol '_min2' shadows an earlier one
    originally declared here

This also immediately happens when min3() or max3() are used.

Since sparse implements __COUNTER__, we can use __UNIQUE_ID() to generate
unique variable names, avoiding this.

Link: http://lkml.kernel.org/r/1471519773-29882-1-git-send-email-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>