scripts/gdb: ensure the absolute path is generated on initial source

Post 'make scripts_gdb' a symbolic link to scripts/gdb/vmlinux-gdb.py is
created.  Currently 'os.path.dirname(__file__)' does not generate the
absolute path to scripts/gdb resulting in the following:

    (gdb) source vmlinux-gdb.py
    Traceback (most recent call last):
      File "scripts/gdb/vmlinux-gdb.py", line 25, in <module>
	import linux.utils
    ModuleNotFoundError: No module named 'linux'

This patch ensures that the absolute path to scripts/gdb in relation to
the given file is generated so each module can be located accordingly.

Link: https://lkml.kernel.org/r/20220712110248.1404125-1-atomlin@redhat.com
Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

scripts/gdb/vmlinux-gdb.py

@@ -13,7 +13,7 @@
 
 import os
 
-sys.path.insert(0, os.path.dirname(__file__) + "/scripts/gdb")
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)) + "/scripts/gdb")
 
 try:
     gdb.parse_and_eval("0")