drm/amd/display: fix type mismatch error for return variable

It is possible for ret_vsnprintf to be assigned negative value in
error cases. As an unsigned variable, negative values which
are stored in their 2's complement form gets treated as a positive
number. This will led to treating bad cases as good ones.
eg: -1 gets stored as 0xFFFFFFFF on a 32 bit system

Signed-off-by: Dale Zhao <dale.zhao@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer_debug.c

@@ -47,7 +47,7 @@
 
 unsigned int snprintf_count(char *pBuf, unsigned int bufSize, char *fmt, ...)
 {
-	unsigned int ret_vsnprintf;
+	int ret_vsnprintf;
 	unsigned int chars_printed;
 
 	va_list args;