spmi: pmic-arb: Return an error code if sanity check fails

If the test 'if (channel > 5)' is true, then we will return 'err' which
is known to be 0 at this point.
Return -EINVAL instead.

Change-Id: I4f558ffb9cde0c9c1127202cd8b5d3ff11987c86
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: e98cc182a06af3b8e91d6d719708db07045d78c4
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: David Collins <collinsd@codeaurora.org>