mm/cma.c: fix a typo ("alloc_cma" -> "cma_alloc") in cma_release() comments

A comment referred to a non-existent function alloc_cma(), which should
have been cma_alloc().

Link: http://lkml.kernel.org/r/20190712085549.5920-1-ryh.szk.cmnty@gmail.comSigned-off-by: Ryohei Suzuki <ryh.szk.cmnty@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/cma.c

@@ -494,7 +494,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
  * @pages: Allocated pages.
  * @count: Number of allocated pages.
  *
- * This function releases memory allocated by alloc_cma().
+ * This function releases memory allocated by cma_alloc().
  * It returns false when provided pages do not belong to contiguous area and
  * true otherwise.
  */