fix: Fix md5 timeout values

This increases the MD5 command timeout factor per megabyte of flash checked
in order to avoid timeouts for flashing bigger images, as the calculation time appears to
increase non-linearly.
A flash size of 4MB was used for testing, and a safety margin of 2 was added.

Author: DNedic

src/esp_loader.c

@@ -46,7 +46,7 @@ static target_chip_t s_target = ESP_UNKNOWN_CHIP;
 
 #if MD5_ENABLED
 
-static const uint32_t MD5_TIMEOUT_PER_MB = 800;
+static const uint32_t MD5_TIMEOUT_PER_MB = 8000;
 static struct MD5Context s_md5_context;
 static uint32_t s_start_address;
 static uint32_t s_image_size;