mx6qsabrelite: README: No need to pass 'u-boot.imx'

The u-boot.imx binary is generated by default, so no need to pass it in the
'make' line.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

board/freescale/mx6qsabrelite/README

@@ -63,7 +63,7 @@ https://wiki.linaro.org/Boards/MX6QSabreLite
 To build U-Boot for the SabreLite board:
 
  make mx6qsabrelite_config
- make u-boot.imx
+ make
 
 To copy the resulting u-boot.imx to the SD card: