mtd: fix memory leak in block2mtd_setup()

There's a mem leak in drivers/mtd/devices/block2mtd.c::block2mtd_setup()

We can leak 'name' allocated with kmalloc in 'parse_name' if leave via
the 'parse_err' macro since it contains a return but doesn't do any
freeing.

Spotted by coverity checker as bug 615.

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>