mshv: Store the result of vfs_poll in a variable of type __poll_t

vfs_poll() returns a result of type __poll_t, but current code is using
an "unsigned int" local variable. The difference is that __poll_t carries
the "bitwise" attribute. This attribute is not interpreted by the C
compiler; it is only used by 'sparse' to flag incorrect usage of the
return value. The return value is used correctly here, so there's no
bug, but sparse complains about the type mismatch.

In the interest of general correctness and to avoid noise from sparse,
change the local variable to type __poll_t. No functional change.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512141339.791TCKnB-lkp@intel.com/


Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>