libfdt: fdt_move(): Fix comparison warnings

With -Wsign-compare, compilers warn about a mismatching signedness
in comparisons in fdt_move().

This stems from "bufsize" being passed in as a signed integer, even
though we would expect a buffer size to be positive.

Short of changing the prototype, check that bufsize is not negative, and
cast it to an unsigned type in the comparison.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-3-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt.c

@@ -314,9 +314,12 @@ const char *fdt_find_string_(const char *strtab, int tabsize, const char *s)
 
 int fdt_move(const void *fdt, void *buf, int bufsize)
 {
+	if (!can_assume(VALID_INPUT) && bufsize < 0)
+		return -FDT_ERR_NOSPACE;
+
 	FDT_RO_PROBE(fdt);
 
-	if (fdt_totalsize(fdt) > bufsize)
+	if (fdt_totalsize(fdt) > (unsigned int)bufsize)
 		return -FDT_ERR_NOSPACE;
 
 	memmove(buf, fdt, fdt_totalsize(fdt));