regulator: dbx500: Remove use of seq_puts/seq_printf return value

The seq_puts/seq_printf return value, because it's frequently misused,
will eventually be converted to void.

See: commit 1f33c41c ("seq_file: Rename seq_overflow() to
     seq_has_overflowed() and make public")

Miscellanea:

o Remove unnecessary dev_err("seq_<foo> overflow\n") messages

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Mark Brown <broonie@kernel.org>