powerpc/ftrace: Fix stack teardown in ftrace_no_trace

Commit 41a506ef ("powerpc/ftrace: Create a dummy stackframe to fix
stack unwind") added use of a new stack frame on ftrace entry to fix
stack unwind. However, the commit missed updating the offset used while
tearing down the ftrace stack when ftrace is disabled. Fix the same.

In addition, the commit missed saving the correct stack pointer in
pt_regs. Update the same.

Fixes: 41a506ef ("powerpc/ftrace: Create a dummy stackframe to fix stack unwind")
Cc: stable@vger.kernel.org # v6.5+
Signed-off-by: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231130065947.2188860-1-naveen@kernel.org

arch/powerpc/kernel/trace/ftrace_entry.S

@@ -62,7 +62,7 @@
 	.endif
 
 	/* Save previous stack pointer (r1) */
-	addi	r8, r1, SWITCH_FRAME_SIZE
+	addi	r8, r1, SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE
 	PPC_STL	r8, GPR1(r1)
 
 	.if \allregs == 1
@@ -182,7 +182,7 @@ ftrace_no_trace:
 	mflr	r3
 	mtctr	r3
 	REST_GPR(3, r1)
-	addi	r1, r1, SWITCH_FRAME_SIZE
+	addi	r1, r1, SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE
 	mtlr	r0
 	bctr
 #endif