i2c: viperboard: return message count on master_xfer success

i2c: viperboard: return message count on master_xfer success

BugLink: http://bugs.launchpad.net/bugs/1794889
[ Upstream commit 35cd67a0caf767aba472452865dcb4471fcce2b1 ]

Returning zero is wrong in this case.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Fixes: 174a13aa8669 ("i2c: Add viperboard i2c master driver")
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>