brcmfmac: fix conversion of channel width 20MHZ_NOHT

The function chandef_to_chanspec() failed when converting a
chandef with bandwidth set to NL80211_CHAN_WIDTH_20_NOHT. This
was reported by user running the device in AP mode.

------------[ cut here ]------------
WARNING: CPU: 0 PID: 304 at
	drivers/net/wireless/brcm80211/brcmfmac/wl_cfg80211.c:381
		chandef_to_chanspec.isra.11+0x158/0x184()

Modules linked in:

CPU: 0 PID: 304 Comm: hostapd Not tainted 3.16.0-rc7-abb+g64aa90f #8

[<c0014bb4>] (unwind_backtrace) from [<c0012314>] (show_stack+0x10/0x14)
[<c0012314>] (show_stack) from [<c001d3f8>] (warn_slowpath_common+0x6c/0x8c)
[<c001d3f8>] (warn_slowpath_common) from [<c001d4b4>] (warn_slowpath_null+0x1c/0x24)
[<c001d4b4>] (warn_slowpath_null) from [<c03449a4>] (chandef_to_chanspec.isra.11+0x158/0x184)
[<c03449a4>] (chandef_to_chanspec.isra.11) from [<c0348e00>] (brcmf_cfg80211_start_ap+0x1e4/0x614)
[<c0348e00>] (brcmf_cfg80211_start_ap) from [<c04d1468>] (nl80211_start_ap+0x288/0x414)
[<c04d1468>] (nl80211_start_ap) from [<c043d144>] (genl_rcv_msg+0x21c/0x38c)
[<c043d144>] (genl_rcv_msg) from [<c043c740>] (netlink_rcv_skb+0xac/0xc0)
[<c043c740>] (netlink_rcv_skb) from [<c043cf14>] (genl_rcv+0x20/0x34)
[<c043cf14>] (genl_rcv) from [<c043c0a0>] (netlink_unicast+0x150/0x20c)
[<c043c0a0>] (netlink_unicast) from [<c043c4b8>] (netlink_sendmsg+0x2b8/0x398)
[<c043c4b8>] (netlink_sendmsg) from [<c04066a4>] (sock_sendmsg+0x84/0xa8)
[<c04066a4>] (sock_sendmsg) from [<c0407c5c>] (___sys_sendmsg.part.29+0x268/0x278)
[<c0407c5c>] (___sys_sendmsg.part.29) from [<c0408bdc>] (__sys_sendmsg+0x4c/0x7c)
[<c0408bdc>] (__sys_sendmsg) from [<c000ec60>] (ret_fast_syscall+0x0/0x44)
---[ end trace 965ee2158c9905a2 ]---

Cc: stable@vger.kernel.org # v3.17
Reported-by: Pontus Fuchs <pontusf@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>