diag: Make fixes to Memory Device mode

Currently the size of the buffer table in diag memory device mode
is set to a predefined value. This patch makes the size of the
buffer table consistent with the maximum number of buffers
possible.

Change-Id: I51313499f7bbe85b589605b7c3b27e27573d1684
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>