wifi: brcmfmac: Add missing Return: to function documentation

wifi: brcmfmac: Add missing Return: to function documentation

Running 'scripts/kernel-doc -Wall -Werror -none' flagged the following
kernel-doc issues:

drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:823: warning: No description found for return value of 'brcmf_apsta_add_vif'
drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:907: warning: No description found for return value of 'brcmf_mon_add_vif'
drivers/net/wireless/broadcom/brcm80211/brcmfmac/cfg80211.c:7419: warning: No description found for return value of 'brcmf_setup_ifmodes'

Add the missing 'Return:' tags to the kernel-doc of these functions.

Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20250106-brcmfmac-kdoc-v1-1-ed72196e21a1@oss.qualcomm.com