libfrog: fix a potential null pointer dereference

libfrog: fix a potential null pointer dereference

Apparently, gcc 10.2 thinks that it's possible for either of the calloc
arguments to be zero here, in which case it will return NULL with a zero
errno.  I suppose it's possible to do that via integer overflow in the
macro, though I find it unlikely unless someone passes in a yuuuge value.

Nevertheless, just shut up the warning by hardcoding the error number
so I can move on to nastier bugs.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>