[PATCH] tools: fdtgrep: Use unsigned chars for arrays

[Samuel Dionne-Riel <samuel@dionne-riel.com>]

Otherwise, values over 127 end up prefixed with ffffff.

Signed-off-by: Samuel Dionne-Riel <samuel@dionne-riel.com>
Cc: Simon Glass <sjg@chromium.org>
---

Minimal reproduction:

```
// repro.dts
/dts-v1/;

/ {
    ra = [ 7f ];
    rb = [ 80 ];
};
```

Steps used to compile:

 $ dtc repro.dts > repro.dtb

Without the fix:

 $ fdtgrep --include-node / repro.dtb
/ {
    ra = [7f];
    rb = [ffffff80];
};

With the fix:

 $ fdtgrep --include-node / repro.dtb
/ {
    ra = [7f];
    rb = [80];
};

---

 tools/fdtgrep.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/fdtgrep.c b/tools/fdtgrep.c
index e4112b8f69..db512465db 100644
--- a/tools/fdtgrep.c
+++ b/tools/fdtgrep.c
@@ -213,7 +213,7 @@ static void utilfdt_print_data(const char *data, int len)
 	} else {
 		printf(" = [");
 		for (i = 0; i < len; i++)
-			printf("%02x%s", *p++, i < len - 1 ? " " : "");
+			printf("%02x%s", (unsigned char)*p++, i < len - 1 ? " " : "");
 		printf("]");
 	}
 }
-- 
2.29.2