msm: mdss: allow get_metadata when the panel is in suspend mode

There are scenarios when HAL retrieves information through get_metadata
when the panel is in suspend mode. Allow the get_metadata ioctl to
go through, even when the panel is in suspend state.

CRs-fixed: 873962
Change-Id: I8d8bd14134f73cb3628e016668e766b818b8d89e
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>