mwifiex: increase max supported pattern offset

The offset number is increased to accomodate requests from
user to match more fields in a Rx packet.

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>