scsi: target: iblock: Fix wrong PR ops NULL check for PREEMPT/RELEASE

In the Linux kernel, the following vulnerability has been resolved: scsi: target: iblock: Fix wrong PR ops NULL check for PREEMPT/RELEASE In the iblock_execute_pr_out() function, PRO_PREEMPT, PRO_PREEMPT_AND_ABORT, and PRO_RELEASE all perform callback capability checks through ops->pr_clear. The error check allows unimplemented hooks to pass through the gate, resulting dereferencing a NULL function pointer. Check whether the hooks that need to be called are supported.