tpm/tpm_ibmvtpm: fix unreachable code warning (smatch warning)

smatch complains:
drivers/char/tpm/tpm_ibmvtpm.c:510
ibmvtpm_crq_process() info: ignoring unreachable code.

-> The return is not necessary here, remove it

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>