staging: rtl8723bs: core: rtw_cmd: drop unneeded null tests

kfree returns immediately on NULL so the tests are not needed.

Generated by: scripts/coccinelle/free/ifnullfree.cocci

CC: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>