Minor bugs in BME280 linux_userspace example code

[lindzey]

Thanks for providing high-quality driver + example code for this chip! It has made my job much easier 😃

There were a handful of issues in linux_userspace.c that I had to fix before getting valid data:

• linux_userspace had the wrong name for an ifdef: BME280_FLOAT_ENABLE needed to be BME280_DOUBLE_ENALBE.  PR#89
• linux_userspace wasn't always using ioctl to set the slave address, so read/writes failed:  PR#92

And a few things that I cleaned up:

• linux_userspace didn't report read failures. PR#90
• there was no need to link against wiringPi. PR#91

I wasn't sure if y'all were open to external contributions, but I went ahead and submitted pull requests for all 4. I submitted them separately to make review as straightforward and independent as possible. Please let me know if you'd prefer them submitted differently.

(I'm using I2C on an ODroid C-4 to read data from the sensor, but I don't think these changes have anything to do with the device used)

[BSTRobin]

Hi lindzey,

Thank for your kindly feedback. I will let our internal team know your pull reuest and evaluate it.

[kgoveas]

Hi @lindzey ,

Thank you for the pull-request. Your changes have been reviewed and merged.