[rcore] fix rpi4 Failed to get DRM resources (#2031)
* [rcore] fix rpi4 Failed to get DRM resources
card1 is not always the the correct card to use on rpi4
rpi os finds the correct card and links it to /dev/dri/by-path/platform-gpu-card during boot.
this fix makes sure that we always point to the correct card on rpi4
* Update rcore.c