driver core: Inline dev_set/get_drvdata

dev_set_drvdata and dev_get_drvdata are now simple enough again that
we can inline them as they used to be before commit b4028437.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>