wcnss: fix the potential memory leak and heap overflow

The wcnss platform driver update the wlan calibration data
by the user space wlan daemon. The wlan user space daemon store
the updated wlan calibration data reported by wlan firmware in
user space and write it back to the wcnss platform calibration
data buffer for the calibration data download and update.

During the wlan calibration data store and retrieve operation
there are some potential race condition which leads to memory leak
and buffer overflow during the context switch.

Fix the above issue by adding protection code and avoid usage of
global pointer during the device file read and write operation.

CRs-Fixed: 2015858
Change-Id: Ib5b57eb86dcb4e6ed799b5222d06396eaabfaad3
Signed-off-by: Sarada Prasanna Garnayak <sgarna@codeaurora.org>