spmi: Auto-populate driver.owner in spmi_driver_register()

Populate the owner field of the spmi driver when
spmi_driver_register() is called in a similar fashion to how
other *_driver_register() functions do it. This saves driver
writers from having to do this themselves.

Cc: Andy Gross <agross@codeaurora.org>
Cc: Gilad Avidov <gavidov@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>