mm: fix some spelling mistakes in comments

Fix some spelling mistakes in comments:
	udpate ==> update
	succesful ==> successful
	exmaple ==> example
	unneccessary ==> unnecessary
	stoping ==> stopping
	uknown ==> unknown

Link: https://lkml.kernel.org/r/20201127011747.86005-1-shihaitao1@huawei.com
Signed-off-by: Haitao Shi <shihaitao1@huawei.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memblock.c b/mm/memblock.c
index 049df41..a3c4060 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -871,7 +871,7 @@ int __init_memblock memblock_physmem_add(phys_addr_t base, phys_addr_t size)
  * @base: base address of the region
  * @size: size of the region
  * @set: set or clear the flag
- * @flag: the flag to udpate
+ * @flag: the flag to update
  *
  * This function isolates region [@base, @base + @size), and sets/clears flag
  *