refcount: Fix a kernel-doc markup

The kernel-doc markup is wrong: it is asking the tool to document
struct refcount_struct, instead of documenting typedef refcount_t.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/afb9bb1e675bf5f72a34a55d780779d7d5916b4c.1606823973.git.mchehab+huawei@kernel.org

include/linux/refcount.h

@@ -101,7 +101,7 @@
 struct mutex;
 
 /**
- * struct refcount_t - variant of atomic_t specialized for reference counts
+ * typedef refcount_t - variant of atomic_t specialized for reference counts
  * @refs: atomic_t counter field
  *
  * The counter saturates at REFCOUNT_SATURATED and will not move once