brcm80211: Avoid possible null-pointer dereferences in wlc_phy_radio_init_2056()

In wlc_phy_radio_init_2056(), regs_SYN_2056_ptr, regs_TX_2056_ptr and
regs_RX_2056_ptr may be not assigned, and thus they are still NULL.
Then, they are used on lines 20042-20050:
    wlc_phy_init_radio_regs(pi, regs_SYN_2056_ptr, (u16) RADIO_2056_SYN);
	wlc_phy_init_radio_regs(pi, regs_TX_2056_ptr, (u16) RADIO_2056_TX0);
	wlc_phy_init_radio_regs(pi, regs_TX_2056_ptr, (u16) RADIO_2056_TX1);
	wlc_phy_init_radio_regs(pi, regs_RX_2056_ptr, (u16) RADIO_2056_RX0);
	wlc_phy_init_radio_regs(pi, regs_RX_2056_ptr, (u16) RADIO_2056_RX1);

Thus, possible null-pointer dereferences may occur.

To avoid these bugs, when these variables are not assigned,
wlc_phy_radio_init_2056() directly returns.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>