cmd: fpga: correct typo, capitalize "Xilinx"

A couple minor tweaks to printed strings in cmd/fpga.c.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/cmd/fpga.c b/cmd/fpga.c
index bc48abd..eba989a 100644
--- a/cmd/fpga.c
+++ b/cmd/fpga.c
@@ -458,7 +458,7 @@
 	   "0-device key, 1-user key, 2-no encryption.\n"
 	   "The optional Userkey address specifies from which address key\n"
 	   "has to be used for decryption if user key is selected.\n"
-	   "NOTE: the sceure bitstream has to be created using xilinx\n"
+	   "NOTE: the secure bitstream has to be created using Xilinx\n"
 	   "bootgen tool only.\n"
 #endif
 );