drm/panfrost: Skip speed binning on EOPNOTSUPP

Encountered on an ARM Mali-T760 MP4, attempting to read the nvmem
variable can also return EOPNOTSUPP instead of ENOENT when speed
binning is unsupported.

Cc: <stable@vger.kernel.org>
Fixes: 7d690f93

 ("drm/panfrost: Add basic support for speed binning")
Signed-off-by: David Michael <fedora.dm0@gmail.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/87msyryd7y.fsf@gmail.com