USB: musb: gadget: fix MUSB_TXMAXP and MUSB_RXMAXP configuration

Commit 9f445cb2[USB: musb: disable
double buffering for older RTL versions] tries to disable double
buffer mode by writing endpoint hw max packet size to TXMAP/RXMAP.

First the approach can break full speed and cause overflow problems.
We should always set those registers with the actual max packet size
from endpoint descriptor.

Second, the problem describe by commit 9f445cb2
was caused by musb gadget driver; nothing to do with RTL revision as
originaly suspected.

The real fix to the problem is to always use actual max packet
size from endpoint descriptor to config TXMAP/RXMAP registers.

Cc: Cliff Cai <cliff.cai@analog.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Anand Gadiyar <gadiyar@ti.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: stable@kernel.org
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>