Fix a bug in the slave serial programming mode for the Xilinx

Spartan2/3 FPGAs. The old code used "< 0" on a "char" type to test if
the most significant bit was set, which did not work on any
architecture where "char" defaulted to be an unsigned type.

Based on a patch by Angelos Manousaridis <amanous@inaccessnetworks.com>

Signed-off-by: Wolfgang Denk <wd@denx.de>

common/spartan2.c

@@ -516,7 +516,7 @@ static int Spartan2_ss_load (Xilinx_desc * desc, void *buf, size_t bsize)
 				(*fn->clk) (FALSE, TRUE, cookie);
 				CONFIG_FPGA_DELAY ();
 				/* Write data */
-				(*fn->wr) ((val < 0), TRUE, cookie);
+				(*fn->wr) ((val & 0x80), TRUE, cookie);
 				CONFIG_FPGA_DELAY ();
 				/* Assert the clock */
 				(*fn->clk) (TRUE, TRUE, cookie);

common/spartan3.c

@@ -521,7 +521,7 @@ static int Spartan3_ss_load (Xilinx_desc * desc, void *buf, size_t bsize)
 				(*fn->clk) (FALSE, TRUE, cookie);
 				CONFIG_FPGA_DELAY ();
 				/* Write data */
-				(*fn->wr) ((val < 0), TRUE, cookie);
+				(*fn->wr) ((val & 0x80), TRUE, cookie);
 				CONFIG_FPGA_DELAY ();
 				/* Assert the clock */
 				(*fn->clk) (TRUE, TRUE, cookie);