spl: x86: Correct the binman symbols for SPL

These symbols are incorrect, meaning that binman cannot find the
associated entry. This leads to errors like:

binman: Section '/binman/simple-bin': Symbol '_binman_spl_prop_size'
   in entry '/binman/simple-bin/u-boot-spl/u-boot-spl-nodtb':
   Entry 'spl' not found in list (mkimage,u-boot-spl-nodtb,
   u-boot-spl-bss-pad,u-boot-spl-dtb,u-boot-spl,u-boot-img,main-section)

Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl.c b/common/spl/spl.c
index 884102b..4449074 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -54,8 +54,8 @@
 binman_sym_declare(ulong, u_boot_any, size);
 
 #ifdef CONFIG_TPL
-binman_sym_declare(ulong, spl, image_pos);
-binman_sym_declare(ulong, spl, size);
+binman_sym_declare(ulong, u_boot_spl, image_pos);
+binman_sym_declare(ulong, u_boot_spl, size);
 #endif
 
 /* Define board data structure */
@@ -143,14 +143,14 @@
 ulong spl_get_image_pos(void)
 {
 	return spl_phase() == PHASE_TPL ?
-		binman_sym(ulong, spl, image_pos) :
+		binman_sym(ulong, u_boot_spl, image_pos) :
 		binman_sym(ulong, u_boot_any, image_pos);
 }
 
 ulong spl_get_image_size(void)
 {
 	return spl_phase() == PHASE_TPL ?
-		binman_sym(ulong, spl, size) :
+		binman_sym(ulong, u_boot_spl, size) :
 		binman_sym(ulong, u_boot_any, size);
 }