include/linux/memblock.h: fix ordering of 'flags' argument in comments

for_each_free_mem_range() and for_each_free_mem_range_reverse() both
accept a 'flags' argument, the comment surrounding the macro placed the
'flags' documentation at the very end, while 'flags' is in fact the 3rd
argument to the macro, so let's preserve natural ordering here.

Fixes: fc6daaf9

 ("mm/memblock: add extra "flags" to memblock to allow selection of memory based on attribute")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>