regulator/mc13783: rename source file to match other drivers

One annoying thing about the old name was that the module was just
called mc13783 which caused wrong expectations (at least for me).

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Liam Girdwood <lrg@slimlogic.co.uk>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>
Acked-by: Mark Brown <broonie@opensoruce.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>