IIO: fix build error in lp8788-charger.c

Turns out that consumer.h needs to include types.h on some platforms to
build properly (like powerpc).

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>