staging:rtl8192u: Refactor DCMD_TXCMD_T structure - Style

The structure DCMD_TXCMD_T is declared with a typedef, which causes a
checkpatch issue with defining new types. As a result the typedef has
been removed.

The structure's name DCMD_TXCMD_T, as a type, is meant to be lowercase
so has been renamed to tx_config_cmd.

The structures three members, (Op, Length, and Value) are all violating
the coding standard policy on CamelCase naming, so have all been renamed.
They have been renamed with longer names, (cmd_op, cmd_length and
cmd_value), to make the variable names easier to search for in code.

The magic numbers '4' and '12' have both been replaced with sizeof()
calls, as they both represent the size of data elements.

These are coding style changes which should have no impact on runtime
code execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>