kvx: gas: fix the detection of negative powers of 2

The detection of negative powers of 2 was wrong and could lead to
well-formed bundles ending up taking more syllables than necessary.

gas/ChangeLog:

	* config/kvx-parse.c (get_token_class): Use the signed value.
	* testsuite/gas/kvx/np2-detection.d: New test.
	* testsuite/gas/kvx/np2-detection.s: New test.
3 files changed