mwifiex: remove unnecessary struct mwifiex_opt_sleep_confirm_buffer

The structure definition is
struct mwifiex_opt_sleep_confirm_buffer {
       u8 hdr[4];
       struct mwifiex_opt_sleep_confirm ps_cfm_sleep;
} __packed;

For sleep_confirm command we already reserve 4 bytes (using skb_reserve())
for an interface header. It will be filled later by interface specific code.
We don't need "hdr[4]" element in above structure. So we can use
"struct mwifiex_opt_sleep_confirm" directly instead of
"struct mwifiex_opt_sleep_confirm_buffer".

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>