Staging: wlan-ng: fix Correct size given to memset

Memset should be given the size of the structure, not the size of the pointer.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
type T;
T *x;
expression E;
@@

memset(x, E, sizeof(
+ *
 x))
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/wlan-ng/prism2fw.c

@@ -439,7 +439,7 @@ void free_chunks(imgchunk_t *fchunk, unsigned int *nfchunks)
 		}
 	}
 	*nfchunks = 0;
-	memset(fchunk, 0, sizeof(fchunk));
+	memset(fchunk, 0, sizeof(*fchunk));
 
 }