power: qpnp-qg: Fix kernel memory corruption error in qg_device_read

qg_device_read function does not validate the count. So, a call
made to this function with data_size greater than count may lead
to kernel memory corruption.

Change-Id: I8b62f94d81317569c04dceec4e9271a77a493d28
Signed-off-by: Ashish Chavan <ashichav@codeaurora.org>