Fixed the comments to match the code and renamed the function to a (hopefully)

more descriptive name, and as per the style guide.

include/busybox.h

@@ -144,7 +144,7 @@ void reset_ino_dev_hashtable(void);
 
 int copyFile(const char *srcName, const char *destName,
 		 int setModes, int followLinks, int forceFlag);
-int copySubFile(int srcFd, int dstFd, size_t remaining);
+int copy_file_chunk(int srcFd, int dstFd, size_t remaining);
 char *buildName(const char *dirName, const char *fileName);
 int makeString(int argc, const char **argv, char *buf, int bufLen);
 char *getChunk(int size);