mm/sparse.c: check __highest_present_section_nr only for a present section

When searching a present section, there are two boundaries:

    * __highest_present_section_nr
    * NR_MEM_SECTIONS

And it is known, __highest_present_section_nr is a more strict boundary
than NR_MEM_SECTIONS.  This means it would be necessary to check
__highest_present_section_nr only.

Link: http://lkml.kernel.org/r/20180326081956.75275-2-richard.weiyang@gmail.comSigned-off-by: NWei Yang <richard.weiyang@gmail.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/sparse.c

@@ -190,15 +190,13 @@ static inline int next_present_section_nr(int section_nr)
 		section_nr++;
 		if (present_section_nr(section_nr))
 			return section_nr;
-	} while ((section_nr < NR_MEM_SECTIONS) &&
-		 (section_nr <= __highest_present_section_nr));
+	} while ((section_nr <= __highest_present_section_nr));
 
 	return -1;
 }
 #define for_each_present_section_nr(start, section_nr)		\
 	for (section_nr = next_present_section_nr(start-1);	\
 	     ((section_nr >= 0) &&				\
-	      (section_nr < NR_MEM_SECTIONS) &&			\
 	      (section_nr <= __highest_present_section_nr));	\
 	     section_nr = next_present_section_nr(section_nr))