mwifiex: report error to MMC core if we cannot suspend

When host_sleep_config command fails we should return error to
MMC core to indicate the failure for our device.

The misspelled variable is also removed as it's redundant.

Cc: "3.0+" <stable@vger.kernel.org>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>