brcm80211: fmac: remove unnecessary NULL pointer check

In brcmf_usb_up() the variable devinfo was checked for being
a NULL pointer, but this can not happen. Also the check was done
after dereferencing the pointer. This patch removes the check.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Kan Yan <kanyan@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>