sh: Fix r7780rp build.

With the addition of the R7780MP and R7785RP, the R7780RP build
ended up breaking. Trivial compile fix.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

include/asm-sh/r7780rp.h

@@ -84,6 +84,7 @@
 #define IRQ_PSW         14              /* Push Switch IRQ */
 
 #elif defined(CONFIG_SH_R7780RP)
+#define PA_POFF		(-1)
 
 #define PA_BCR		0xa5000000	/* FPGA */
 #define	PA_IRLMSK	(PA_BCR+0x0000)	/* Interrupt Mask control */