rtlwifi: always initialize variables given to RT_TRACE()

In rtl_rx_ampdu_apply(), when rtlpriv->cfg->ops->get_btc_status()
returns false, RT_TRACE() is called with the values of variables
reject_agg and agg_size, which have not been initialized.

Always initialize these variables in order to prevent using
uninitialized values.

This issue has been found with clang. The compiler reported:

    drivers/net/wireless/realtek/rtlwifi/base.c:1665:6: error: variable
    'agg_size' is used uninitialized whenever 'if' condition is false
    [-Werror,-Wsometimes-uninitialized]
            if (rtlpriv->cfg->ops->get_btc_status())
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/net/wireless/realtek/rtlwifi/base.c:1671:31: note:
    uninitialized use occurs here
                     reject_agg, ctrl_agg_size, agg_size);
                                                ^~~~~~~~

    drivers/net/wireless/realtek/rtlwifi/base.c:1665:6: error: variable
    'reject_agg' is used uninitialized whenever 'if' condition
          is false [-Werror,-Wsometimes-uninitialized]
            if (rtlpriv->cfg->ops->get_btc_status())
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/net/wireless/realtek/rtlwifi/base.c:1671:4: note:
    uninitialized use occurs here
                     reject_agg, ctrl_agg_size, agg_size);
                     ^~~~~~~~~~

Fixes: 2635664e ("rtlwifi: Add rx ampdu cfg for btcoexist.")
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>