vfio/fsl-mc: Make vfio_fsl_mc_irqs_allocate static

Fixed compiler warning:
drivers/vfio/fsl-mc/vfio_fsl_mc_intr.c:16:5: warning: no previous
prototype for function 'vfio_fsl_mc_irqs_allocate' [-Wmissing-prototypes]
       ^
drivers/vfio/fsl-mc/vfio_fsl_mc_intr.c:16:1: note: declare 'static'
if the function is not intended to be used outside of this translation unit
int vfio_fsl_mc_irqs_allocate(struct vfio_fsl_mc_device *vdev)

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Diana Craciun <diana.craciun@oss.nxp.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>