libfrog: change project entity variable scope to local/static.

libfrog: change project entity variable scope to local/static.

The project quota code used a global variable "p" for getprent() and
getprpathent(), presumably to keep the interface analogous to getpwent()
etc.  However, other functions had their own local "p" which led to shadow
variable warnings from sparse.

Rather than a global, make it a static variable within the project
functions.  Same behavior, same interface, less confusion, and retains an
interface similar that of getpwent etc.

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