mshv: fix SRCU protection in irqfd resampler ack handler

mshv: fix SRCU protection in irqfd resampler ack handler

Replace hlist_for_each_entry_rcu() with hlist_for_each_entry_srcu()
in mshv_irqfd_resampler_ack() to correctly handle SRCU-protected
linked list traversal.

The function uses SRCU (sleepable RCU) synchronization via
partition->pt_irq_srcu, but was incorrectly using the RCU variant
for list iteration. This could lead to race conditions when the
list is modified concurrently.

Also add srcu_read_lock_held() assertion as required by
hlist_for_each_entry_srcu() to ensure we're in the proper
read-side critical section.

Fixes: 621191d709b14 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
Acked-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>