msm: camera: cpp: Check for valid tx level

TX and RX FIFOs of Microcontroller are used to exchange commands
and messages between Micro FW and CPP driver. TX FIFO depth is
16 32-bit words, incase of errors there is a chance of overflow.
To prevent possible out of bound access, TX FIFO depth or
level is checked for MAX depth before accessing the FIFO.

Change-Id: I5adf39b46ff10e358c4a2c03a2de07d44b99cedb
Signed-off-by: Pratap Nirujogi <pratapn@codeaurora.org>