virtiofsd: Changed allocations of fv_VuDev & its internals to GLib functions

Changed the allocations of fv_VuDev structs, VuDev structs, and
fv_QueueInfo strcuts from using calloc()/realloc() & free() to using
the equivalent functions from GLib.

In instances, removed the pair of allocation and assertion for
non-NULL checking with a GLib function that aborts on error.

Removed NULL-checking for fv_VuDev struct allocation and used
a GLib function that crashes on error; namely, g_new0(). This
is because allocating one struct should not be a problem on an
healthy system. Also following the pattern of aborting-on-null
behaviour that is taken with allocating VuDev structs and
fv_QueueInfo structs.

Signed-off-by: Mahmoud Mandour <ma.mandourr@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210420154643.58439-6-ma.mandourr@gmail.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>