msm: adsprpc: use correct size while copying user data

Currently, an uninitialized size variable is being used to copy
data from user. Use correct size while copying user concurrency
info for enabling persistent headers.

Change-Id: Ie81305060f2f278b29def11508cdc9851677d33e
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Himateja Reddy <hmreddy@codeaurora.org>