wifi: rtw89: fw: move v1 MSSC out of __parse_security_section() to share with v0

The security section can be a common parser for v0 and v1 format of
firmware header, so move retrieval code of v1 MSSC from the function, and
then sharing becomes possible.

Not logic change at all.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20241030022135.11688-7-pkshih@realtek.com