msm: mdss: On sharing dma pipe increment pipe ref_cnt

When DMA pipe is being shared and if mdss_mdp_pipe_map is called,
there could be a race condition when the pipe being shared
is unmapped, will lead to map failure as map is used for operations
on pipe which are already having positive ref_cnt.
This can result in potential map failure and attempt to free of
unmapped pipe resulting in crash.

Hence in this scenario of shared pipe usage atomic_inc should
be used instead of mdss_mdp_pipe_map.

CRs-Fixed: 590736
Change-Id: Ibaba20ac96662b5cd8aba3585f10d9cfe6e72d22
Signed-off-by: Justin Philip <jphili@codeaurora.org>