qr: bitstream: remove unused spinlock field from bitstream struct

I added it to test some SMP functionality, but since libqr is bugged
to hell on SMP, let us remove it until we fix it.

Signed-off-by: Levente Kurusa <levex@linux.com>
qr: bitstream: use the bitstream's GFP for allocating the byte array

Signed-off-by: Levente Kurusa <levex@linux.com>
qr: bitstream: rename _data field to data

I renamed data to _data while debugging during rewriting the bitstream
code, but since it's considered stable now, let us rename it back.

Signed-off-by: Levente Kurusa <levex@linux.com>
qr: bitstream: fix build warning

I forgot to add a 'return 0;' statement to the end of the append
function. Add that now.

Fixes: 821370f ("qr: bitstream: rewrite to use 8 times less memory")
Signed-off-by: Levente Kurusa <levex@linux.com>