utils: os_unix: Use access() for checking file existence

Trying to open file for checking file existence seems to be too much.
Instead use access system call which is meant for the same.

Signed-off-by: Rahul Bedarkar <rahulbedarkar89@gmail.com>

src/utils/os_unix.c

@@ -435,11 +435,7 @@ char * os_readfile(const char *name, size_t *len)
 
 int os_file_exists(const char *fname)
 {
-	FILE *f = fopen(fname, "rb");
-	if (f == NULL)
-		return 0;
-	fclose(f);
-	return 1;
+	return access(fname, F_OK) == 0;
 }