scripts/gdb: fix dentry_name() lookup

scripts/gdb: fix dentry_name() lookup

The "d_iname" member was replaced with "d_shortname.string" in the commit
referenced in the Fixes tag.  This prevented the GDB script "lx-mount"
command to properly function:

(gdb) lx-mounts
      mount          super_block     devname pathname fstype options
0xff11000002d21180 0xff11000002d24800 rootfs / rootfs rw 0 0
0xff11000002e18a80 0xff11000003713000 /dev/root / ext4 rw,relatime 0 0
Python Exception <class 'gdb.error'>: There is no member named d_iname.
Error occurred in Python: There is no member named d_iname.

Link: https://lkml.kernel.org/r/20250619225105.320729-1-florian.fainelli@broadcom.com
Fixes: 58cf9c383c5c ("dcache: back inline names with a struct-wrapped array of unsigned long")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>