ARM: at91: fix typo in at91_pmc_base assembly declaration

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/include/mach/at91_pmc.h

@@ -25,7 +25,7 @@ extern void __iomem *at91_pmc_base;
 #define at91_pmc_write(field, value) \
 	__raw_writel(value, at91_pmc_base + field)
 #else
-.extern at91_aic_base
+.extern at91_pmc_base
 #endif
 
 #define	AT91_PMC_SCER		0x00			/* System Clock Enable Register */