Use "#!/bin/sh" instead of ":" in tools/gen-offsets.sh.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/tools/gen-offsets.sh b/tools/gen-offsets.sh
index 99fdc53..73dede8 100755
--- a/tools/gen-offsets.sh
+++ b/tools/gen-offsets.sh
@@ -1,4 +1,4 @@
-:
+#!/bin/sh
 # Extract definitions from an assembler file.  This is based on code
 # from the Linux Kernel.
 INFILE=$1