drm/gma500: fix a missing break in psb_intel_crtc_mode_set

Instead of exiting the loop as expected when an entry is found, the
list_for_each_entry() continues until the traversal is complete.
when found the entry, add a break after the switch statement.

Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220401115018.9335-1-xiam0nd.tong@gmail.com