meta-ibm: palmetto: rename phosphor-hwmon bbappend

Rename phosphor-hwmon%.bbappend to phosphor-hwmon_%.bbappend.

Tested: Built palmetto and verified rootfs contained sensor confs.
Change-Id: Ib6ed5e568656028ee1d993cff96cdc26e34f6c8e
Signed-off-by: Patrick Venture <venture@google.com>
4 files changed