coresight-tmc: Fix span multiple pages error during tmc_read

The length from tmc_sg_table_get_data can't be more than one page
size. Otherwise issue will happen when do user_copy.

Change-Id: I23a98f79c3b299deada22fbd12d3e9ffd91fd309
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>