wifi: rtw89: fw: get sb_sel_ver via get_unaligned_le32()

The sb_sel_ver is selection version for secure boot recorded in firmware
binary data, and its size is 4 and offset is 58 (not natural alignment).
Use get_unaligned_le32() to get this value safely. Find this by reviewing.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250217064308.43559-3-pkshih@realtek.com