This reverts commit 5083fd7bdf.
A bulk-out size smaller than the end-point size is indeed valid. The
offending commit broke the usb-debug driver for EHCI debug devices,
which use 8-byte buffers.
Fixes: 5083fd7bdf ("USB: serial: make bulk_out_size a lower limit")
Reported-by: "Li, Elvin" <elvin.li@intel.com>
Cc: stable <stable@vger.kernel.org> # v3.15
Signed-off-by: Johan Hovold <johan@kernel.org>