driver core: platform: Don't read past the end of "driver_override" buffer

When printing the driver_override parameter when it is 4095 and 4094 bytes
long, the printing code would access invalid memory because we need count+1
bytes for printing.

Reject driver_override values of these lengths in driver_override_store().

This is in close analogy to commit 4efe874a ("PCI: Don't read past the
end of sysfs "driver_override" buffer") from Sasha Levin.

Fixes: 3d713e0e ("driver core: platform: add device binding path 'driver_override'")
Cc: stable@vger.kernel.org	# v3.17+
Signed-off-by: Nicolai Stange <nstange@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>