soc: ti: smartreflex: Simplify getting the opam_sr pointer

The probe function stores the sr_info pointer using
platform_set_drvdata(). Use the corresponding platform_get_drvdata() to
retrieve that pointer in the remove and shutdown functions.

This simplifies these functions and makes error handling unnecessary.
This is a good thing as at least for .remove() returning an error code
doesn't have the desired effect.

This is a preparation for making platform remove callbacks return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>