mwifiex: fix make namespacecheck warnings

This patch takes care of warnings found by running
'make namespacecheck':

1. Remove dead code.
2. Reorder function definitions to avoid forward declarations.
3. Remove unnecessary function/structure declarations and mark
   them as static.

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