mwifiex: report error to MMC core if we cannot suspend

commit dd321acddc3be1371263b8c9e6c6f2af89f63d57 upstream.

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.

Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>