power: smb5: Modify VOLTAGE_QNOVO write behaviour

Allow QNOVO_VOTER to take precedence over BATT_PROFILE_VOTER when a
valid value is written to VOLTAGE_QNOVO.

Change-Id: I2c81cb87ae331ebdc94eec11be7524f36b6ed2e4
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>