coresight-byte-cntr: Fix the Byte-Counter read operation

The tmc struct has two entries: memtype and mem_type. Where
mem_type attribute contains the mem_type sysfs node value
and memtype attribute contains the ETR mode of operation
chosen at the etr memory allocation. The byte cntr read
operation should use the memtype value.

Change-Id: Ia9c8bdfa858e85ba777217806625a156960932b3
Signed-off-by: Saranya Chidura <schidura@codeaurora.org>