brcmfmac: fix sdio sg table alloc crash

With commit 7d34b056 ("brcmfmac: Move all module parameters to
one place") a bug was introduced causing a null pointer exception.
This patch fixes the bug by initializing the sg table till after
the settings have been initialized.

Fixes: 7d34b056 ("brcmfmac: Move all module parameters to one place")
Reported-by: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>