staging: vchiq_core: introduce handle_poll

The function slot_handler_func() has very deep indentations. Moving the
poll handling into separate function could improve the readability.
Use the return value to keep the poll_needed handling at the same place.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Link: https://lore.kernel.org/r/1622735405-9980-17-git-send-email-stefan.wahren@i2se.com


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