git-compat-util: fix documentation syntax

The parameter marker for x was garbled in its introduction in 89c855ed3c
("git-compat-util.h: implement a different ARRAY_SIZE macro for for
safely deriving the size of array", 2015-04-30).

Signed-off-by: Beat Bolli <dev+git@drbeat.li>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -77,7 +77,7 @@
 #endif
 /*
  * ARRAY_SIZE - get the number of elements in a visible array
- *  <at> x: the array whose size you want.
+ * @x: the array whose size you want.
  *
  * This does not work on pointers, or arrays declared as [], or
  * function parameters.  With correct compiler support, such usage