powerpc/52xx: Fix an invalid ASM expression ('addi' used instead of 'add')

AS arch/powerpc/platforms/52xx/lite5200_sleep.o
arch/powerpc/platforms/52xx/lite5200_sleep.S: Assembler messages:
arch/powerpc/platforms/52xx/lite5200_sleep.S:184: Warning: invalid register expression

In the following code, 'addi' is wrong, has to be 'add'

/* local udelay in sram is needed */
udelay: /* r11 - tb_ticks_per_usec, r12 - usecs, overwrites r13 */
mullw r12, r12, r11
mftb r13 /* start */
addi r12, r13, r12 /* end */

Fixes: ee983079ce04 ("[POWERPC] MPC5200 low power mode")
Signed-off-by: Christophe Leroy <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/cb4cec91[e-mail]

arch/powerpc/platforms/52xx/lite5200_sleep.S

···
   udelay: /* r11 - tb_ticks_per_usec, r12 - usecs, overwrites r13 */
 	mullw	r12, r12, r11
 	mftb	r13	/* start */
-	addi	r12, r13, r12 /* end */
+	add	r12, r13, r12 /* end */
     1:
 	mftb	r13	/* current */
 	cmp	cr0, r13, r12