wcnss: fix the potential buffer flow issue in firmware setup

Add the check against negative or invalid firmware size passed
by the userspace thread in firmware setup sysfs write operation.
Update the datatype of the variable which holds the firmware size
passed by userspace thread during firmware setup and WLAN calibration
data update process.

CRs-Fixed: 2072966
Change-Id: I8c84ad0d1b0a5f44a39c9c5b228734b0f693e8dd
Signed-off-by: Sarada Prasanna Garnayak <sgarna@codeaurora.org>