drivers/fm: Fix compiling error if FW location is not defined

FMAN firmware can be in NOR flash, NAND flash, SPI flash, MMC or even
remote. In case none of them is defined, set it to null.

Signed-off-by: York Sun <yorksun@freescale.com>

drivers/net/fm/fm.c

@@ -396,6 +396,8 @@ int fm_init_common(int index, struct ccsr_fman *reg)
 	}
 #elif defined(CONFIG_SYS_QE_FMAN_FW_IN_REMOTE)
 	void *addr = (void *)CONFIG_SYS_QE_FMAN_FW_ADDR;
+#else
+	void *addr = NULL;
 #endif
 
 	/* Upload the Fman microcode if it's present */