staging: et131x: Rename var name 'etdev' to 'adapter' throughout module

Used regex (from vim) :%s/\<etdev\>/adapter/g

Changed because:
* 'etdev' is easily confused as a misspelling of 'netdev'
* 'adapter' is more widely used for this struct type in net drivers. This
change made comparing code with other drivers much easier.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>