mm: mmap: fix a typo in comment "compatbility"->"compatibility"

There is a typo in comment, fix it.
Signed-off-by: Ethon Paul <ethp@qq.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Link: http://lkml.kernel.org/r/20200410163206.14016-1-ethp@qq.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -1207,7 +1207,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 }
 
 /*
- * Rough compatbility check to quickly see if it's even worth looking
+ * Rough compatibility check to quickly see if it's even worth looking
  * at sharing an anon_vma.
  *
  * They need to have the same vm_file, and the flags can only differ