power: qpnp-qnovo5: Echo back value written to standalone

The "standalone" class parameter which when read returns whether the
charge pumps are enabled or not. Change this to simply echo back the
value written to it by userspace.

Change-Id: Idb44d99967691b1cd3315004ea0b5f7034e8e376
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>