mwifiex: update comment for shutdown_sw()/reinit_sw() to reflect current state

The functions mwifiex_shutdown_sw() and mwifiex_reinit_sw() can be used
for more general purposes than the PCIe function level reset. Also, these
are even not PCIe-specific.

So, let's update the comments at the top of each function accordingly.

Signed-off-by: Tsuchiya Yuto <kitakar@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201028142110.18144-3-kitakar@gmail.com