rsi: Delete unnecessary variable initialisation

In rsi_send_data_pkt(), the following variables are assigned to
before they're used:

 * tmp_hdr - Assigned on line 47, first used on line 48
 * bss - Assigned on line 41, first used on line 44
 * extnd_size - Assigned on line 50, first used on line 52
 * seq_num - Assigned on line 48, first used on line 96

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
[Rewrote commit message]
Signed-off-by: Julian Calaby <julian.calaby@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>