brcmfmac: fix wrong num_different_channels when mchan feature enabled

When the device/firmware supports multi-channel, it can have P2P
connection and regular connection with AP simultaneous. In this case,
the num_different_channels in wiphy info was not correct when firmware
supports multi-channel (The iw wiphy# info showed "#channels <= 1" in
interface combinations). It caused association failed and error message
"CTRL-EVENT-FREQ-CONFLICT error" in wpa_supplicant when P2P GO interface
was running at the same time.
The root cause is that the num_different_channels was always overridden
to 1 in brcmf_setup_ifmodes even multi-channel was enabled.
We correct the logic by moving num_different_channels setting forward.

Signed-off-by: Wright Feng <wright.feng@cypress.com>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>