samples: environmental sensing: fix BMP280 kconfig options

Update the prj.conf file, as the driver and Kconfig options for the BMP280
sensor were renamed to BME280 the following commit:
	310ed1e2 sensor: add support for BME280

Change-Id: If3d81d90c269883aa51ff04a12f8fd1aa444a592
Signed-off-by: Bogdan Davidoaia <bogdan.m.davidoaia@intel.com>