mshv: Use EPOLLIN and EPOLLHUP instead of POLLIN and POLLHUP

mshv: Use EPOLLIN and EPOLLHUP instead of POLLIN and POLLHUP

mshv code currently uses the POLLIN and POLLHUP flags. Starting with
commit a9a08845e9acb ("vfs: do bulk POLL* -> EPOLL* replacement") the
intent is to use the EPOLL* versions throughout the kernel.

The comment at the top of mshv_eventfd.c describes it as being inspired
by the KVM implementation, which was changed by the above mentioned
commit in 2018 to use EPOLL*. mshv_eventfd.c is much newer than 2018
and there's no statement as to why it must use the POLL* versions.
So change it to use the EPOLL* versions. This change also resolves
a 'sparse' warning.

No functional change, and the generated code is the same.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601220948.MUTO60W4-lkp@intel.com/
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>