rtl8192u: fix printk calls in r8192U_core.c

This patch replaces calls to printk with their
corresponding calls to pr_<loglevel>(fmt, ...)
and netdev_<loglevel>(dev, fmt, ...), when it
is applicable, to make the log messages more
informative.

Also, it fixes some small typos and whitespaces
found in log messages.

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>