CHROMIUM: mfd: chromeos_ec: remove compilation warning

CHROMIUM: mfd: chromeos_ec: remove compilation warning

Really confusing since it warns for use in the function called:

drivers/mfd/chromeos_ec.c: In function 'cros_ec_command_xfer':
drivers/mfd/chromeos_ec.c:156:6: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]

BUG=none
TEST=build, make sure warning is gone

Change-Id: Ib21c8a90a20a71ede9a2458a83f1d530b619c20a
Signed-off-by: Olof Johansson <olofj@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/28128
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>