gas/testsuite: adjust a test for case insensitive file systems

gas/testsuite: adjust a test for case insensitive file systems

When dealing with case insensitive file systems, ".file line.s" and
".file Line.s" are identical and thus gas won't change the current
input file.
However, in line.l test, it's expecting to trigger an input file switch.
As the second filename doesn't matter in it, change it to fit for those
file systems.

gas/ChangeLog:

	* testsuite/gas/elf/line.l: Change Line.s to Line2.s.
	* testsuite/gas/elf/line.s: Adjust output.