cadence_gem: Fix Rx buffer size field mask

This patch corrects the Rx buffer size field mask to mask bits 23 to 16
to match Xilinx UG585 documentation.
Signed-off-by: NSai Pavan Boddu <saipava@xilinx.com>
Reviewed-by: NAlistair Francis <alistair.francis@xilinx.com>
Reviewed-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/net/cadence_gem.c

@@ -155,7 +155,7 @@
 #define GEM_NWCFG_BCAST_REJ    0x00000020 /* Reject broadcast packets */
 #define GEM_NWCFG_PROMISC      0x00000010 /* Accept all packets */
 
-#define GEM_DMACFG_RBUFSZ_M    0x007F0000 /* DMA RX Buffer Size mask */
+#define GEM_DMACFG_RBUFSZ_M    0x00FF0000 /* DMA RX Buffer Size mask */
 #define GEM_DMACFG_RBUFSZ_S    16         /* DMA RX Buffer Size shift */
 #define GEM_DMACFG_RBUFSZ_MUL  64         /* DMA RX Buffer Size multiplier */
 #define GEM_DMACFG_TXCSUM_OFFL 0x00000800 /* Transmit checksum offload */