Use the correct register when storing the arm VFP state.

Previously we have been lucky where the state was already in r0, however
this is not guaranteed. Use the passed in register as the location to
store the upper half of the arm VFP registers rather than relying on it
being r0.

Approved by:	re (kib)

sys/arm/arm/vfp.c

@@ -293,7 +293,7 @@ vfp_store(struct vfp_state *vfpsave, boolean_t disable_vfp)
 		    " .fpu	vfpv3\n"
 		    " vstmia	%0!, {d0-d15}\n"	/* d0-d15 */
 		    " cmp	%1, #0\n"		/* -D16 or -D32? */
-		    " vstmiane	r0!, {d16-d31}\n"	/* d16-d31 */
+		    " vstmiane	%0!, {d16-d31}\n"	/* d16-d31 */
 		    " addeq	%0, %0, #128\n"		/* skip missing regs */
 		    : "+&r" (vfpsave) : "r" (is_d32) : "cc"
 		    );