ARM: entry: avoid clobbering R9 in IRQ handler

Avoid using R9 in the IRQ handler code, as the entry code uses it for
tsk, and expects it to remain untouched between the IRQ entry and exit
code.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/arm/kernel/entry-armv.S

@@ -38,11 +38,10 @@
 #ifdef CONFIG_UNWINDER_ARM
 	mov	fpreg, sp		@ Preserve original SP
 #else
-	mov	r8, fp			@ Preserve original FP
-	mov	r9, sp			@ Preserve original SP
+	mov	r7, fp			@ Preserve original FP
+	mov	r8, sp			@ Preserve original SP
 #endif
 	ldr_this_cpu sp, irq_stack_ptr, r2, r3
-
 	.if	\from_user == 0
 UNWIND(	.setfp	fpreg, sp		)
 	@
@@ -82,8 +81,8 @@ UNWIND(	.setfp	fpreg, sp		)
 #ifdef CONFIG_UNWINDER_ARM
 	mov	sp, fpreg		@ Restore original SP
 #else
-	mov	fp, r8			@ Restore original FP
-	mov	sp, r9			@ Restore original SP
+	mov	fp, r7			@ Restore original FP
+	mov	sp, r8			@ Restore original SP
 #endif // CONFIG_UNWINDER_ARM
 #endif // CONFIG_IRQSTACKS
 	.endm