SPL ext: cosmetic: correct error message in spl_load_image_ext()

Correct the error message in spl_load_image_ext() when image parsing
fails. Instead of "ext4fs_read failed" print "failed to parse image
header".
Signed-off-by: NPetr Kulhavy <brain@jikos.cz>
CC: Guillaume GARDET <guillaume.gardet@free.fr>
CC: Tom Rini <trini@konsulko.com>

common/spl/spl_ext.c

@@ -50,7 +50,7 @@ int spl_load_image_ext(struct blk_desc *block_dev,
 
 	err = spl_parse_image_header(header);
 	if (err < 0) {
-		puts("spl: ext4fs_read failed\n");
+		puts("spl: ext: failed to parse image header\n");
 		goto end;
 	}