mm/sparse.c: pass the __highest_present_section_nr + 1 to alloc_func()

mm/sparse.c: pass the __highest_present_section_nr + 1 to alloc_func()

In commit c4e1be9ec113 ("mm, sparsemem: break out of loops early")
__highest_present_section_nr is introduced to reduce the loop counts for
present section.  This is also helpful for usemap and memmap allocation.

This patch uses __highest_present_section_nr + 1 to optimize the loop.

Link: http://lkml.kernel.org/r/20180326081956.75275-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>