mm/sparse: fix a bad comparison

next_present_section_nr() could only return an unsigned number -1, so
just check it specifically where compilers will convert -1 to unsigned
if needed.

mm/sparse.c: In function 'sparse_init_nid':
mm/sparse.c:200:20: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
((section_nr >= 0) && \
^~
mm/sparse.c:478:2: note: in expansion of macro
'for_each_present_section_nr'
for_each_present_section_nr(pnum_begin, pnum) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/sparse.c:200:20: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
((section_nr >= 0) && \
^~
mm/sparse.c:497:2: note: in expansion of macro
'for_each_present_section_nr'
for_each_present_section_nr(pnum_begin, pnum) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/sparse.c: In function 'sparse_init':
mm/sparse.c:200:20: warning: comparison of unsigned expression >= 0 is always true [-Wtype-limits]
((section_nr >= 0) && \
^~
mm/sparse.c:520:2: note: in expansion of macro
'for_each_present_section_nr'
for_each_present_section_nr(pnum_begin + 1, pnum_end) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: c4e1be9ec113 ("mm, sparsemem: break out of loops early")
Signed-off-by: Qian Cai <[e-mail]>
Reviewed-by: Andrew Morton <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/sparse.c

···
 }
 #define for_each_present_section_nr(start, section_nr)		\
 	for (section_nr = next_present_section_nr(start-1);	\
-	     ((section_nr >= 0) &&				\
+	     ((section_nr != -1) &&				\
 	      (section_nr <= __highest_present_section_nr));	\
 	     section_nr = next_present_section_nr(section_nr))