misc: cxl: clean up afu_read_config()

The sanity checks for overflow are not needed, because this is done on
caller side in fs/sysfs/file.c

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Cc: Ian Munsie <imunsie@au1.ibm.com>
Acked-by: Michael Neuling <mikey@neuling.org>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>