misc/pvpanic-mmio: Fix error handling in 'pvpanic_mmio_probe()'

There is no error handling path in the probe function.
Switch to managed resource so that errors in the probe are handled easily
and simplify the remove function accordingly.

Fixes: b3c0f877

 ("misc/pvpanic: probe multiple instances")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/2a5dab18f10db783b27e0579ba66cc38d610734a.1621665058.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>