regmap: debugfs: Fix a erroneous check after snprintf()

This error handling looks really strange.
Check if the string has been truncated instead.

Fixes: f0c2319f ("regmap: Expose the driver name in debugfs")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/8595de2462c490561f70020a6d11f4d6b652b468.1693857825.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Mark Brown <broonie@kernel.org>