msm: mdss: Fix memleak in framebuffer register and remove

In FB registration, free allocated memory
if an error condition is hit. Also free
allocated memory in FB remove.

Change-Id: I533e2d6a760ebd52047c521c1a1e85bfc754fce1
Signed-off-by: Krishna Srinivas <krisrini@codeaurora.org>