usertools: fix syntax warning in python 3.8

Silent the following warning when running script with python 3.8:

> /usr/bin/dpdk-pmdinfo:542: SyntaxWarning: "is" with a literal.
> Did you mean "=="?
>   if (autoload_path is None or autoload_path is ""):

As autoload_path can only be None or a string, directly check its bool
value.

Fixes: c67c9a5c64 ("tools: query binaries for HW and other support information")
Cc: stable@dpdk.org

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>

usertools/dpdk-pmdinfo.py

@@ -539,7 +539,7 @@ def scan_for_autoload_pmds(dpdk_path):
         return
 
     (autoload_path, scannedfile) = readelf.search_for_autoload_path()
-    if (autoload_path is None or autoload_path is ""):
+    if not autoload_path:
         if (raw_output is False):
             print("No autoload path configured in %s" % dpdk_path)
         return