drm/amd/display: Check otg_master pointer before use it

drm/amd/display: Check otg_master pointer before use it

Coverity highlighted that the parameter otg_master is referenced before
the if condition that validates it, which means that the code might have
some attempt to access a null pointer. This commit addresses this issue
by moving the pointer verification to the beginning of the function and
initializing all the values right after it.

Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>