scsi: core: pair EH runtime PM get and put

In the Linux kernel, the following vulnerability has been resolved:

scsi: core: pair EH runtime PM get and put

shost->eh_noresume is currently consulted twice in one error handling
iteration: once before scsi_autopm_get_host() and once again before
scsi_autopm_put_host().

That is racy when a PM-triggered error path flips shost->eh_noresume
while the SCSI EH thread is still running.

The problem flow looks like this:
PM path
ufshcd_set_dev_pwr_mode()
shost->eh_noresume = 1
ufshcd_execute_start_stop <-- trigger EH
...
shost->eh_noresume = 0

EH path
scsi_error_handler()
if (!shost->eh_noresume)
scsi_autopm_get_host() <-- skipped
...
if (!shost->eh_noresume)
scsi_autopm_put_host() <-- executed later

In that case one EH iteration can skip autoresume on entry and still
drop a runtime PM reference on exit. That leaves an unmatched runtime PM
put and can trigger a runtime PM usage count underflow.

Fix this by making eh_noresume a regular bool so it can be accessed with
READ_ONCE() and WRITE_ONCE(). Snapshot it once per EH iteration and use
that snapshot for both runtime PM get and put decisions.