staging: hisi-spmi-controller: rename spmi-channel property

The spmi-channel is not used on other drivers. So, rename it,
in order to document that this is specific to those devices.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/ed45fc5d84d7b531343ee5d3466ebfac26217da0.1624542940.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>