soc/intel/common: Check bios_size and window_size after MIN operation

Clang Static Analyzer version 8.0.0 detects that the result of
log2_ceil(bios_size) and log2_ceil(window_size) is undefined if the
value of bios_size and window_size are negative. Add negative value
Check for bios_size and window_size after MIN operation.

Change-Id: I28577b6e0ba0ab45bb7804c17ba1f26c4b078b15
Signed-off-by: John Zhao <john.zhao@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34182
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/intel/common/block/fast_spi/fast_spi.c

@@ -241,7 +241,7 @@ void fast_spi_cache_bios_region(void)
 	 * protection, so limit the cached bios region to be no more than 16MB.
 	 * */
 	bios_size = MIN(bios_size, 16 * MiB);
-	if (!bios_size)
+	if (bios_size <= 0)
 		return;
 
 	/* Round to power of two */

src/soc/intel/common/block/lpc/lpc_lib.c

@@ -80,7 +80,7 @@ void lpc_open_pmio_window(uint16_t base, uint16_t size)
 		/* Each IO range register can only open a 256-byte window. */
 		window_size = MIN(size, LPC_LGIR_MAX_WINDOW_SIZE);
 
-		if (!window_size)
+		if (window_size <= 0)
 			return;
 
 		/* Window size must be a power of two for the AMASK to work. */