tpm: Store devname in the tpm_chip

Just put the memory directly in the chip structure, rather than
in a 2nd dedicated kmalloc.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Reviewed-by: Joel Schopp <jschopp@linux.vnet.ibm.com>
Reviewed-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Acked-by: Ashley Lai <adlai@linux.vnet.ibm.com>