mwifiex: remove redundant timestamps in debug prints

We don't need wall-clock time here, and in most configurations
that care, there are already timestamps in the kernel using
CONFIG_PRINTK_TIME=y.

Reported-by: Paul Stewart <pstew@chromium.org>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>