sunrpc: simplify rpcauth_cache_shrink_count()

It is inappropriate to use sysctl_vfs_cache_pressure here.
The sysctl is documented as: This percentage value controls
the tendency of the kernel to reclaim the memory which is used
for caching of directory and inode objects.

So, simplify result of rpcauth_cache_shrink_count() to
"return number_cred_unused;".

Signed-off-by: Kaixiong Yu <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Acked-by: Anna Schumaker <[e-mail]>
Acked-by: Jeff Layton <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Joel Granados <[e-mail]>

net/sunrpc/auth.c

···
 rpcauth_cache_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 
 {
-	return number_cred_unused * sysctl_vfs_cache_pressure / 100;
+	return number_cred_unused;
 }
 
 static void