staging: ks7010: add variables key, key_index

'auth_type - 1' is used as an index into a key table. Adding a variable
appropriately named simplifies the code and adds meaning when
reading. Adding a pointer variable of type struct *kpa_key_t adds to
readability by removing the table access each time the key is used.

The key index is used to create a string so having it named adds
additional meaning when creating the string.

Declare variable 'key_index' and define it at declaration time. Declare
a pointer variable 'key' and define it to point to the correct key in
the key table.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>