msm: mdss: fb: remove check for allocated during resolution switch

While switching resolution the fb memory requirement may increase and
the current memory may not be able to support the new resolution.
However since we can still go through overlay path, this requirement
shouldn't be mandatory. Allow it to go through, there are enough
checks during mmap to fail if trying to use this memory.

Change-Id: I76aafecd568763c456ea75234582b8a7aa9f83f4
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>