usb: musb: change rxcsr register from write to read/modify/write

The RX Control/Status register has bits that we want to preserve, so don't
just write out a single bit.  Preserve the others bits in the process.

The original code posted to the u-boot list had this behavior, but looks
like it was lost somewhere along the way to merging.
Signed-off-by: NBryan Wu <bryan.wu@analog.com>
Signed-off-by: NCliff Cai <cliff.cai@analog.com>
Signed-off-by: NMike Frysinger <vapier@gentoo.org>
Signed-off-by: NRemy Bohmer <linux@bohmer.net>

drivers/usb/musb/musb_hcd.c

@@ -604,7 +604,8 @@ int submit_bulk_msg(struct usb_device *dev, unsigned long pipe,
 					(len-txlen) : dev->epmaxpacketin[ep];
 
 			/* Set the ReqPkt bit */
-			writew(MUSB_RXCSR_H_REQPKT, &musbr->rxcsr);
+			csr = readw(&musbr->rxcsr);
+			writew(csr | MUSB_RXCSR_H_REQPKT, &musbr->rxcsr);
 
 			/* Wait until the RxPktRdy bit is set */
 			if (!wait_until_rxep_ready(dev, MUSB_BULK_EP)) {
@@ -775,7 +776,8 @@ int submit_int_msg(struct usb_device *dev, unsigned long pipe,
 					(len-txlen) : dev->epmaxpacketin[ep];
 
 			/* Set the ReqPkt bit */
-			writew(MUSB_RXCSR_H_REQPKT, &musbr->rxcsr);
+			csr = readw(&musbr->rxcsr);
+			writew(csr | MUSB_RXCSR_H_REQPKT, &musbr->rxcsr);
 
 			/* Wait until the RxPktRdy bit is set */
 			if (!wait_until_rxep_ready(dev, MUSB_INTR_EP)) {