iio.h: Undef the __api macro after declarations of API functions
iio.h: Undef the __api macro after declarations of API functions

Signed-off-by: Paul Cercueil <73d292422978d45c9eeef455bb1b24a0db453722@analog.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,gburca/libiio,analogdevicesinc/libiio,gburca/libiio,gburca/libiio