virt: acrn: Fix document of acrn_msi_inject()

virt: acrn: Fix document of acrn_msi_inject()

This fixes below build warning with extra build checks.

$ make W=1

../drivers/virt/acrn/vm.c:105: warning: expecting prototype for
acrn_inject_msi(). Prototype was for acrn_msi_inject() instead

Fixes: c7cf8d27244f ("virt: acrn: Introduce interrupt injection interfaces")
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Link: https://lore.kernel.org/r/20210311015206.19715-1-shuo.a.liu@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>