Regulator: lp3972 cleanup

This patch includes below fixes based on Mark's comment.
 - Return actual error if i2c_smbus_read_byte_data() fail
 - Add spaces around bitwise AND operator(&) to improve readability
 - Add comment to explain why we need to update voltage change control register
   for LDO1 and LDO5
 - Logging the value for diagnostics if chip reported incorrect voltage value
 - Add __devinit annotation for setup_regulators()
 - Show system control register1 value if the value is mismatched
 - Logging the value for diagnostics if failed to detect device

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>