Remove unneeded stack writes

src/mod.S

@@ -11,9 +11,7 @@ line_count:     .space 6
 # @param[out] a0: result code.
 # @param[out] a1: bytes written to mod buf.
 add_endings:
-    addi sp, sp, -72
-    sd s7, 64(sp)
-    sd s6, 56(sp)
+    addi sp, sp, -56
     sd s5, 48(sp)
     sd s4, 40(sp)
     sd ra, 32(sp)
@@ -63,9 +61,7 @@ add_endings:
     ld ra, 32(sp)
     ld s4, 40(sp)
     ld s5, 48(sp)
-    ld s6, 56(sp)
-    ld s7, 64(sp)
-    addi sp, sp, 72
+    addi sp, sp, 56
     ret
 
 # Prefix newlines with ######+TAB line count
@@ -76,8 +72,7 @@ add_endings:
 # @param[out] a0: result code.
 # @param[out] a1: bytes written to mod buf.
 add_line_numbers:
-    addi sp, sp, -72
-    sd s7, 64(sp) #unused
+    addi sp, sp, -64
     sd s6, 56(sp) # mod buf ptr
     sd s5, 48(sp) # mod buf bp
     sd s4, 40(sp) # str buf ptr
@@ -170,8 +165,7 @@ add_line_numbers:
     ld s4, 40(sp)
     ld s5, 48(sp)
     ld s6, 56(sp)
-    ld s7, 64(sp)
-    addi sp, sp, 72
+    addi sp, sp, 64
     ret