The 'ratp_command_ctx' seems to specify that this variable is only
used to process command operations, but it really is used in every
async operation (e.g. also in FS), so just rename it to a more generic
name for clarity.

Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>