staging: rtl8723bs: cleanup NULL check before vfree

Remove redundant NULL pointer check before vfree() since vfree() does
its own NULL check. Reported by coccinelle.

Signed-off-by: Amarjargal Gundjalam <amarjargal16@gmail.com>
Link: https://lore.kernel.org/r/20201026141510.GA21791@AJ-T14


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>