scsi: mpt3sas: Fix error return value in _scsih_expander_add()

scsi: mpt3sas: Fix error return value in _scsih_expander_add()

When an expander does not contain any 'phys', an appropriate error code -1
should be returned, as done elsewhere in this function. However, we
currently do not explicitly assign this error code to 'rc'. As a result, 0
was incorrectly returned.

Link: https://lore.kernel.org/r/20210514081300.6650-1-thunder.leizhen@huawei.com
Fixes: f92363d12359 ("[SCSI] mpt3sas: add new driver supporting 12GB SAS")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>