staging: rtl8723bs: hal: rtl8723b_cmd: fix Comparison to NULL

This patch fixes below issues reported by checkpatch

CHECK: Comparison to NULL could be written "psta"
CHECK: Comparison to NULL could be written
"pmlmepriv->wps_probe_resp_ie"
CHECK: Comparison to NULL could be written "psta"

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>