mwifiex: debugfs: allow card_reset() to cancel things

The card_reset() implementation should be setting our state flags and
cancelling commands for us (i.e., in mwifiex_shutdown_drv()), so let's
not do it here.

Also, this debugfs file is useful for testing and debugging the reset
feature, so we shouldn't do extra preparatory steps here, as that might
cause different reset behavior, which could either cause new bugs or
paper over existing ones that this debug feature should otherwise help
us catch.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>