staging: rtl8723bs: split multiple assignment in rtw_mgmt_xmitframe_coalesce

staging: rtl8723bs: split multiple assignment in rtw_mgmt_xmitframe_coalesce

Cleanup the multiple assignment of tmp_buf and BIP_AAD to fix the
checkpatch.pl CHECK: "Multiple assignments should be avoided".

Additionally, reorder the assignments to ensure tmp_buf is assigned
only after BIP_AAD has been validated as non-NULL.

Signed-off-by: Marco Antonio Solis Segura <mshdevv@gmail.com>
Link: https://patch.msgid.link/20260319062626.605200-1-mshdevv@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>