intel_edison_fab_c.c: If i2c bus number is invalid use the default bus (6)

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
spi: fix mraa_spi_bit_per_word call to use correct ioctl

This should fix #14

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
syslog: unify error msg style

syslog messages should be written as <module>: Message in order to increase
readability and usefulness

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>