staging: r8192U_core: Remove unused variable 'ret' and demote kernel-doc abuse

staging: r8192U_core: Remove unused variable 'ret' and demote kernel-doc abuse

Fixes the following W=1 kernel build warning(s):

 drivers/staging/rtl8192u/r8192U_core.c: In function ‘rtl8192_hard_data_xmit’:
 drivers/staging/rtl8192u/r8192U_core.c:905:6: warning: variable ‘ret’ set but not used [-Wunused-but-set-variable]

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Andrea Merello <andrea.merello@gmail.com>
Cc: Jerry chuang <wlanfae@realtek.com>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210414181129.1628598-2-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>