staging: et131x: Audit and update comments

Many of the functions and variables in the driver have been renamed and are now
more readable, as well as defines added for various constants. Update / remove
some comments to reflect this.

Also many comments were unnecessary dialogue describing what is evident from
the code, or comments were just plain incorrect, remove these too.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
staging: et131x: Simplify for loop in et131x_init_send()

The for loop in this function increments two variables and has an unusual
starting index of 1 (not 0). Make it look more familiar.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mark Einon <mark.einon@gmail.com>