usb: cdns3: gadget: suspicious implicit sign extension

The code:
trb->length = cpu_to_le32(TRB_BURST_LEN(priv_ep->trb_burst_size)
	       	| TRB_LEN(length));

TRB_BURST_LEN(priv_ep->trb_burst_size) may be overflow for int 32 if
priv_ep->trb_burst_size is equal or larger than 0x80;

Below is the Coverity warning:
sign_extension: Suspicious implicit sign extension: priv_ep->trb_burst_size
with type u8 (8 bits, unsigned) is promoted in priv_ep->trb_burst_size << 24
to type int (32 bits, signed), then sign-extended to type unsigned long
(64 bits, unsigned). If priv_ep->trb_burst_size << 24 is greater than 0x7FFFFFFF,
the upper bits of the result will all be 1.

To fix it, it needs to add an explicit cast to unsigned int type for ((p) << 24).

Reviewed-by: Jun Li <jun.li@nxp.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>