Fix uninitialized variable in ipmb_dev_int.c

ret at line 112 of ipmb_dev_int.c is uninitialized which
results in a warning during build regressions.
This warning was found by build regression/improvement
testing for v5.3-rc1.

Reported-by: build regression/improvement testing for v5.3-rc1.
Fixes: 51bd6f29

 ("Add support for IPMB driver")
Signed-off-by: Asmaa Mnebhi <Asmaa@mellanox.com>
Message-Id: <571dbb67cf58411d567953d9fb3739eb4789238b.1563996586.git.Asmaa@mellanox.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>