brcmfmac: Clarify if using braces.

Whilst this if () statement is technically correct, it lacks clarity.

Signed-off-by: Ian Molton <ian@mnementh.co.uk>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>