drm/amd/display: Remove else after return in 'dm_crtc_get_scanoutpos()'

Conform to Linux kernel coding style.

Reported by checkpatch:

WARNING: else is not generally useful after a break or return

Expressions under 'else' branch in function 'dm_crtc_get_scanoutpos' are
executed whenever the expression in 'if' is False. Otherwise, return
from function occurs. Therefore, there is no need in 'else', and it has
been removed.

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>