fpga: Fix spelling mistake "eXchnage" -> "exchange" in Kconfig

There is a spelling mistake in the Kconfig text. Fix it.
Reviewed-by: Tom Rix <trix@redhat.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

drivers/fpga/Kconfig

@@ -119,7 +119,7 @@ config XILINX_PR_DECOUPLER
 	depends on HAS_IOMEM
 	help
 	  Say Y to enable drivers for Xilinx LogiCORE PR Decoupler
-	  or Xilinx Dynamic Function eXchnage AIX Shutdown Manager.
+	  or Xilinx Dynamic Function eXchange AIX Shutdown Manager.
 	  The PR Decoupler exists in the FPGA fabric to isolate one
 	  region of the FPGA from the busses while that region is
 	  being reprogrammed during partial reconfig.