s390/pai_crypto: Rename PAI Crypto event 4210

The PAI crypto event number 4210 is named
   PCC_COMPUTE_LAST_BLOCK_CMAC_USING_ENCRYPTED_AES_256A
According to the z16 and z17 Principle of Operation documents
SA22-7832-13 and SA22-7832-14 the event is named
   PCC_COMPUTE_LAST_BLOCK_CMAC_USING_ENCRYPTED_AES_256
without a trailing 'A'.
Adjust this event name.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>