[powerpc*] Revert "fbdev/offb: Update expected device name"

Commit 241d2fb56a18 "of: Make OF framebuffer device names unique", included in Linux 6.2 and backported to 6.1.12, changed the Linux platform device names for OpenFirmware "display" device nodes on powerpc from "of-display" to "of-display.0", "of-display.1", etc. This caused them to no longer match the offb device driver, though it's not entirely clear why since they should match through the compatible string.. This was reported as Debian bug #1033058.

Our patch "fbdev/offb: Update expected device name" was supposed to fix bug that by changing the driver name of offb to "of-display.0", matching the new first device name.

Later, commit 0bb8f49cd2cc "of: Preserve "of-display" device name for compatibility", included in Linux 6.5 and backported to 6.1.42, reverted the first device name to be "of-display" again.

The combination of both changes means the device and driver names are mismatched again, resulting in bug #1085949.

Drop our patch.

Closes: #1085949