staging/rtl8192u: avoid Wempty-body warning

staging/rtl8192u: avoid Wempty-body warning

This driver has a few disabled diagnostics, which can probably
just get removed, or might still be helpful:

drivers/staging/rtl8192u/r8192U_core.c: In function 'rtl8192_set_rxconf':
drivers/staging/rtl8192u/r8192U_core.c:767:45: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
  767 |                 DMESG("NIC in promisc mode");
      |                                             ^
drivers/staging/rtl8192u/r8192U_core.c: In function 'rtl819xusb_rx_command_packet':
drivers/staging/rtl8192u/r8192U_core.c:883:80: error: suggest braces around empty body in an 'if' statement [-Werror=empty-body]
  883 |                 DMESG("rxcommandpackethandle819xusb: It is a command packet\n");
      |                                                                                ^

Changing the empty macro to no_printk() to shut up the compiler warnings
and add format string checking.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210322103545.704121-1-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>