brcmfmac: fix spelling mistake "Retreiving" -> "Retrieving"

Trivial fix to spelling mistake in brcmf_err error message.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>