powerpc/44x: Fix mask and shift to zero bug

My static checker complains that 0x00001800 >> 13 is zero. Looking at
the context, it seems like a copy and paste bug from the line below
and probably 0x3 << 13 or 0x00006000 was intended.

Fixes: 2af59f7d5c3e ("[POWERPC] 4xx: Add 405GPr and 405EP support in boot wrapper")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/boot/4xx.c

@@ -564,7 +564,7 @@ void ibm405gp_fixup_clocks(unsigned int sys_clk, unsigned int ser_clk)
 		fbdv = 16;
 	cbdv = ((pllmr & 0x00060000) >> 17) + 1; /* CPU:PLB */
 	opdv = ((pllmr & 0x00018000) >> 15) + 1; /* PLB:OPB */
-	ppdv = ((pllmr & 0x00001800) >> 13) + 1; /* PLB:PCI */
+	ppdv = ((pllmr & 0x00006000) >> 13) + 1; /* PLB:PCI */
 	epdv = ((pllmr & 0x00001800) >> 11) + 2; /* PLB:EBC */
 	udiv = ((cpc0_cr0 & 0x3e) >> 1) + 1;