regmap: Properly round reg_bytes and val_bytes

For the upcoming 2/6-format, we don't see debugfs output otherwise,
since the current division results in 0. I'd think 10/14 is broken
currently, too.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>