ptserver: Simplify malloc assignment to shut up clang

ptserver: Simplify malloc assignment to shut up clang

Using a temporary variable of type (char *) to store the results
of malloc and realloc, and then casting the tmp variable to the
real type causes clang-analyzer to complain. Just simplify this
code by always using the real type in order to shut it up.

Change-Id: I607bb36d1899dc617fdbd9e09e18ff10c9fa9ce9
Reviewed-on: http://gerrit.openafs.org/9148
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>