Bluetooth: Do not shadow hdr variable

Fix compile warnings below:

...
net/bluetooth/a2mp.c:505:33: warning: symbol 'hdr' shadows an earlier one
net/bluetooth/a2mp.c:498:25: originally declared here
...

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>