am43xx_evm.h: Correct SPL max size

Upon further inspection of relevant parts of the architecture, the
maximum SPL binary size is 220KiB.

Cc: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/include/configs/am43xx_evm.h b/include/configs/am43xx_evm.h
index 4de495a..83431a4 100644
--- a/include/configs/am43xx_evm.h
+++ b/include/configs/am43xx_evm.h
@@ -34,7 +34,7 @@
 
 /* SPL defines. */
 #define CONFIG_SPL_TEXT_BASE		0x40300350
-#define CONFIG_SPL_MAX_SIZE		(0x40337C00 - CONFIG_SPL_TEXT_BASE)
+#define CONFIG_SPL_MAX_SIZE		(220 << 10)	/* 220KB */
 #define CONFIG_SPL_YMODEM_SUPPORT
 
 /* Enabling L2 Cache */