hwmon: VRM is not written to registers

What was true of reading the VRM value is also true of writing it: not
being a register value, it doesn't need hardware access, so we don't
need a reference to the i2c client. This allows for a minor code
cleanup. As gcc appears to be smart enough to simplify the generated
code by itself, this cleanup only affects the source code, the
generated binaries are unchanged.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>