ld: don't use ia64 register name in expression of pr16322 test

ld: don't use ia64 register name in expression of pr16322 test

"f1" is a register name on ia64, and hence gets warned upon when used
as expression value:

.../binutils/2.25/ld/testsuite/ld-elf/pr16322.s: Assembler messages:
.../binutils/2.25/ld/testsuite/ld-elf/pr16322.s:6: Warning: register value used as expression

Change the name (and "p1" at once, which is a register name too, albeit
not currently causing any immediate problem).

ld/testsuite/
2015-01-28  Jan Beulich  <jbeulich@suse.com>

	* ld-elf/pr16322.s (p1): Rename to px1.
	(f1): Rename to fx1.