ipmi:bt-bmc: Fix error handling and status check

ipmi:bt-bmc: Fix error handling and status check

If the function platform_get_irq() failed, the negative value
returned will not be detected here. So fix error handling in
bt_bmc_config_irq(). And in the function bt_bmc_probe(),
when get irq failed, it will print error message. So use
platform_get_irq_optional() to simplify code. Finally in the
function bt_bmc_remove() should make the right status check
if get irq failed.

Signed-off-by: Shengju Zhang <zhangshengju@cmss.chinamobile.com>
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Message-Id: <20200505102906.17196-1-tangbin@cmss.chinamobile.com>
[Also set bt_bmc->irq to a negative value if devm_request_irq() fails.]
Signed-off-by: Corey Minyard <cminyard@mvista.com>