brcmfmac: fix use of skb control buffer in SDIO driver part

The SDIO driver has a 16-bit field defined in the skbuff control buffer.
However, it is accessed as a u32 overwriting other control info. Another
issue is that the field is not initialized for networking packets, but
the control buffer content is unspecified as other networking layers can
use it.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>