diag: Update mask buffer after reallocation

Currently, reallocated mask update buffers are not
updated if the received mask range is more than the
mask update buffer length. Update the reallocated buffer
address before writing the mask to peripherals.

CRs-Fixed: 2266693
Change-Id: I6b506ce68e17b7da61926b0f9543157812a8c555
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>