Change field name according to Java naming convention

The Java naming convention claims:
Constants should be written in uppercase characters separated by
underscores. Constant names may also contain digits if appropriate, but
not as the first character.

Convert field names to uppercase according to the naming convention.

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Reviewed-by: Bastian Germann <bage@linutronix.de>