mwifiex: correct max IE length check for WPS IE

This patch is bug fix for an invalid boundry check for WPS IE.
We should check max IE length against defined macro; instead we were
checking it against size of pointer. Fix it.
Also move IE length check before allocation of memory.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>