UPSTREAM: mwifiex: correction in mcs index check

UPSTREAM: mwifiex: correction in mcs index check

mwifiex driver supports 2x2 chips as well. Hence valid mcs values
are 0 to 15. The check for mcs index is corrected in this patch.

For example: if 40MHz is enabled and mcs index is 11, "iw link"
command would show "tx bitrate: 108.0 MBit/s" without this patch.
Now it shows "tx bitrate: 108.0 MBit/s MCS 11 40Mhz" with the patch.

Cc: "3.2.y, 3.3.y, 3.4.y" <stable@vger.kernel.org>
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>
BUG=chrome-os-partner:12190
TEST=Build and run autotest WiFiMatFunc, WiFiSecMat, WiFiManager, WiFiPerf

Change-Id: I4ec246b8d8e9a1f36eb3caa4438e19076dc3f8bd
Reviewed-on: https://gerrit.chromium.org/gerrit/29094
Reviewed-by: Sam Leffler <sleffler@chromium.org>
Tested-by: Bing Zhao <bzhao@marvell.com>
Commit-Ready: Bing Zhao <bzhao@marvell.com>