pipeline: fix build with glibc < 2.26

pipeline: fix build with glibc < 2.26

reallocarray has been introduced in glibc 2.26 but we still support
glibc >= 2.7.
Simply replace with realloc, as the considered sizes are unlikely to
overflow.

"""
The reallocarray() function changes the size of the memory block
pointed to by ptr to be large enough for an array of nmemb elements,
each of which is size bytes.  It is equivalent to the call

       realloc(ptr, nmemb * size);

However, unlike that realloc() call, reallocarray() fails safely in
the case where the multiplication would overflow.  If such an over‐
flow occurs, reallocarray() returns NULL, sets errno to ENOMEM, and
leaves the original block of memory unchanged.
"""

Fixes: 3ca60ceed79a ("pipeline: add SWX pipeline specification file")

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>