switcher: NFC: .Lout_of_trusted_stack zero a1 with the others

Co-authored-by: David Chisnall <github@theravensnest.org>

sdk/core/switcher/entry.S

diff --git a/sdk/core/switcher/entry.S b/sdk/core/switcher/entry.S
index 98085d6..f9302c9 100644
--- a/sdk/core/switcher/entry.S
+++ b/sdk/core/switcher/entry.S
@@ -414,11 +414,10 @@
 	clc                cra, SPILL_SLOT_pcc(csp)
 	clc                cgp, SPILL_SLOT_cgp(csp)
 	cincoffset         csp, csp, SPILL_SLOT_SIZE
-	// Set the return registers
+	// Set the first return register (a0) and zero the other (a1) below
 	li                 a0, -ENOTENOUGHTRUSTEDSTACK
-	li                 a1, 0
 	// Zero everything else
-	zeroAllRegistersExcept ra, sp, gp, s0, s1, a0, a1
+	zeroAllRegistersExcept ra, sp, gp, s0, s1, a0
 	cret
 
 .size compartment_switcher_entry, . - compartment_switcher_entry