wl1271: use __packed annotation

This patch changes __attribute__ ((packed)) annotations to __packed in wl1271
code that was introduced in a recent patch in wireless-testing.

Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>