wifi: rtw89: coex: initialize local .dbcc_2g_phy in _set_btg_ctrl()

For the case of DBCC enabled and fwrole version 0, the local variable
wl_rinfo.dbcc_2g_phy might not be set by following for-loop, leading
uninitialized variable before using.

Addresses-Coverity-ID: 1586724 ("Uninitialized scalar variable")

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20240919081216.28505-3-pkshih@realtek.com