drm/amd/display: Check denominator crb_pipes before used

commit ea79068d upstream.

[WHAT & HOW]
A denominator cannot be 0, and is checked before used.

This fixes 2 DIVIDE_BY_ZERO issues reported by Coverity.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Cliff Liu <donghua.liu@windriver.com>
Signed-off-by: He Zhe <Zhe.He@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>