mshv: pass struct mshv_user_mem_region by reference

mshv: pass struct mshv_user_mem_region by reference

For unstated reasons, function mshv_partition_ioctl_set_memory passes
struct mshv_user_mem_region by value instead of by reference. Change
it to pass by reference.

Signed-off-by: Mukesh R <mrathor@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>