staging: r8188eu: Fix potential memory leak or NULL dereference

In routine c2h_wk_callback(() following a kmalloc() call, the
error recovery is flawed. If the kmalloc() returns a pointer
that is not NULL, and the following c2h_evt_read() fails, the
code will leak that buffer. If the kmalloc() fails, a NULL
dereference will occur in the following code.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Link: https://lore.kernel.org/r/20210806213235.22349-1-Larry.Finger@lwfinger.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/core/rtw_cmd.c

@@ -1908,9 +1908,13 @@ static void c2h_wk_callback(struct work_struct *work)
 			c2h_evt = kmalloc(16, GFP_KERNEL);
 			if (c2h_evt) {
 				/* This C2H event is not read, read & clear now */
-				if (c2h_evt_read(adapter, (u8 *)c2h_evt) != _SUCCESS)
+				if (c2h_evt_read(adapter, (u8 *)c2h_evt) != _SUCCESS) {
+					kfree(c2h_evt);
 					continue;
 				}
+			} else {
+				return;
+			}
 		}
 
 		/* Special pointer to trigger c2h_evt_clear only */