scsi: core: Remove unreachable code warning

The smatch tool reported the following warning:
drivers/scsi/scsi_error.c:1988 scsi_decide_disposition() warn: ignoring
unreachable code.

Remove the "default:return FAILED;" instead of "return FAILED;" reported by
smatch, because compilers can provide more useful diagnostics about
switch/case statements that do not have a default statement, especially if
the "switch" applies to a value with enumeration type.

Link: https://lore.kernel.org/r/20220301080448.112813-1-yang.lee@linux.alibaba.com


Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>