samples: drivers: change hard-coded device name

Change to use the device name defined by driver's Kconfig for
device binding, instead of hard-coding it which is not portable.

Jira: ZEP-1764

Change-Id: I0dc9aa2cdf426af71f1ed6dcef1ec7cec19f4c3e
Signed-off-by: Kuo-Lang Tseng <kuo-lang.tseng@intel.com>
(cherry picked from commit e90aa43e)